Do you always need to tip 20%? Here's how much an etiquette expert says to leave at restaurants, hotels and more

We've all been there. The barista hands you your coffee and spins their tablet around to show a screen that prompts you to tip 15%, 20%, 30% or 0% on your order.

It's an experience that's become commonplace beyond places where it was previously considered normal to tip, and Americans are getting fed up. In fact, 2 in 3 Americans now have a negative view of the entire tipping practice, a recent Bankrate survey found.

There are two basic reasons it might feel like you're being asked for tips more frequently:

1. Technology: Digital cash register tablets and other new technologies have made it easier for customers to give tips and for businesses to receive them in an increasingly cashless society.
2. The gig economy: The average consumer can now outsource countless tasks, from getting your dog groomed to having an employee bring your Target order to your car, creating more opportunities than ever to tip a person who does a service for you.

"We're using more services, so of course we are confronted with more tipping opportunities," Diane Gottsman, founder of The Protocol School in Texas and a nationally-recognized etiquette expert, tells CNBC Make It.

But do you have to tip everyone every time? Gottsman says no. Here's when you should actually be tipping — and how much.

How much to tip at restaurants

In the U.S., tipping at restaurants is almost universally expected.

In most states, tipped workers — who are often servers, bartenders and other hospitality staff — earn a minimum wage significantly lower than the regular federal minimum wage. Customer tips are expected to make up the difference.

Here's how much to tip in various situations.

Sitting down for a meal: Always tip 15% to 20%

These rules haven't changed much. Gottsman and other industry experts still recommend tipping 15% to 20% on your bill when you have a sit-down meal at a restaurant.

"If you're going to a restaurant, you know that part of your experience is going to be gratuity," Gottsman says. "[When] you're paying for the meal, you also factor in the gratuity."

Having food delivered: $5 minimum

Even if you're staying home and having your food delivered, you should still be tipping, Gottsman says. She recommends giving at least $5 for a typical order.

"You want to give [delivery drivers] a minimum of $5 even if it's a small order," she says. "If it's a large order and they're carrying boxes of food to you and your soccer team, you want to tip accordingly — 15% of that bill, if they have really worked hard to get it to you."

Sitting at the bar: It depends

If you're sitting at the bar, use similar guidelines based on what you're ordering. Gottsman says $1 to $2 for a beer or cocktail is acceptable, but to still tip 15% to 20% of your tab if you're ordering snacks or food.

When the service is bad: Still leave a tip

Regardless of how much you tip, it should be a number you're comfortable with, both economically and emotionally. Tipping, especially at restaurants, reflects your experience with a server, says Douglass Miller, a restaurant management professor at Cornell University's Nolan School of Hotel Administration.

If you felt the service was subpar, it's still kind to leave a tip, but it's OK to listen to your gut, he says.

"Part of it is understanding if service has gone bad, where it's gone bad — it may or may not have anything to do with the server," Miller says. "I tell people that they should tip what they're comfortable with — I don't force them, but if you create an environment and provide an experience where they get value, majority of the time [customers] will tip accordingly."

How much to tip on vacation

When you're traveling, Gottsman says you should always leave a tip for valets, bellhops, housekeepers and shuttle drivers.

"Those are complimentary services, but they're not really complimentary because the housekeeper is working for gratuities, and the valet is working for that gratuity, and so is the shuttle driver," Gottsman says. "They will be getting paid an hourly wage rate as well, but gratuity really helps there, it's part of the standard."

You can stick to a dollar or two per bag for a shuttle driver or $2 if they're not handling your luggage, Gottsman says. Hand $2 to $3 to your bellhop for the first bag and another dollar or two for each additional bag. If the bellhop takes your bag to your room, she recommends a minimum $3 tip.

For valet drivers, "$3 to $5 is standard unless you are requesting a special service, such as leaving the car upfront while you run into the hotel," Gottsman says. "Then give them $5 to $10. Even if there is a fee for valet service, you still tip the valet."

She also recommends leaving $3 to $5 a day in your hotel room for housekeeping services, and leaving a tip every day rather than just at the end because it will likely be a new staff member every time.

You don't always have to tip

Although opportunities to tip are everywhere — and seem to be increasing in number — it's not always required, Gottsman says.

"There are some industries where you'll want to tip, but there's other industries that if you'd like to tip, by all means go ahead, but it's not necessary," she says.

"If you go to a fast food restaurant and you order a burger, you don't have to leave a tip," for example. The same goes for coffee shops or other quick-service places where you might be faced with the dreaded tablet screen. 

This is where common sense comes in handy, Gottsman says. But humanity is important too, she adds — if you're feeling generous, go ahead and leave a tip.

"If you experienced great service from this person, if there's a connection between [you and] them, they're smiling, they're friendly, and you feel the urge to tip, by all means do so," Gottsman says.

"I never want to discourage a tip, but if you have a six-second exchange — you ask for a cup of coffee, they turn around, pour it from the spout, and hand it to you — that is discretionary," she adds.

If you feel pressured from the tablet screens or receipts that tell you how much to tip based on your bill, Gottsman recommends carrying cash in small bills. You can still leave a tip, but give yourself a limit you're comfortable with and be able to hit the "no tip" button without feeling rude.

DON'T MISS: Want to be smarter and more successful with your money, work & life? Sign up for our new newsletter!

Get CNBC's free Warren Buffett Guide to Investing, which distills the billionaire's No. 1 best piece of advice for regular investors, do's and don'ts, and three key investing principles into a clear and simple guidebook.