UPDATE 2-Tax gains lift Merck, but sales disappoint

*3rd- qtr EPS, excluding items, $0.95, vs $0.92 forecast. Oct 26- Merck& Co Inc reported a higher-than-expected third-quarter profit, as a favorable tax rate and lower merger costs helped offset plunging sales of its former flagship product, Singulair, an asthma drug that began facing cheaper generics in August.