At Restaurants: Leave as close to 10 percent as is convenient, but no more.

At Hotels: Porters, 5 euros; housekeepers, 1–2 euros per night, more for extra service.
(or 15–20 percent of the tab).

Who Else?: Despite the old-world romance of a ride on the canal, tipping gondoliers and vaporettos isn't customary.

Dollars Accepted?: Yes, but euros are much preferred.

P.S. "There is no fixed percentage as in the U.S.," says Filippo Curinga, of Italy-based IDI Travel. Another travel agent recommends insisting if your tip is first refused—it's a common demurral in Italy.

Source : CNTraveler.com