The yen hit a one-month high against the dollar on Tuesday, buoyed by steady demand for safe-haven assets against a backdrop of plunging oil prices.
Sterling recovered some ground on Friday, pushing back above $1.51 as the dollar retreated broadly.
The euro extended losses into a sixth straight day to trade near a nine-year low, as investors bet the ECB was getting closer to adopting QE.
The euro hit another nine-year low against the dollar on Wednesday, after data for the euro zone revealed that prices were falling in the region.
The U.K. pound hit a fresh 17-month low against the U.S. dollar on Tuesday and currency experts are split on which way the currency will head next.
The safe-haven yen rose as investor risk aversion mounted following a sharp drop in crude oil and stocks.
The euro fell to near a nine-year low, hit by concerns that Greek elections will result in a government that will aim to cancel austerity measures.
The euro fell to its lowest in 4-1/2 years against the dollar on Friday after the head of the ECB fanned expectations of QE later this month.
The U.S. dollar hit its highest level since March 2006 on Friday, as the euro fell on speculation about imminent monetary easing tactics.
The dollar was set to end 2014 with a gain of more than 12 percent against a basket of major currencies on Wednesday.
The yen gained sharply against both the dollar and euro on Tuesday as investors sought the traditional safety of the Japanese currency.
The euro inched up but remained near two-year-lows after a key vote in Greece failed to secure a new president.
The dollar edged up against the yen on Friday on light bargain hunting, with markets slowly getting into gear after the Christmas holiday.
Currency strategists are pondering whether there is more volatility in store for the ruble.
The dollar hovered at its highest in nearly nine years after strong U.S. economic growth caused market speculation of earlier interest rate hike.
The euro bounced back from two-year lows against a slightly weaker dollar on Monday, with Greece's election among risks to a calmer mood.
The U.S. dollar rose against major currencies for a third session on diverging monetary policy between the Federal Reserve and other central banks.
The dollar pared gains against major currencies on Wednesday after the Fed said there remains "considerable time" before an interest rate hike.
The U.S. dollar slipped against major currencies on Tuesday on expectations that the Federal Reserve would take a cautious tone.
Emergency measures by the Russian central bank Monday night looked to have fallen short within hours of their announcement.