when traveling and trying to save every penny possible.

Under-tipping and over-tipping can both be considered offensive depending on what country you are in. The main rule to stick with when in doubt is never tip for bar/counter service, and add about 10 percent for a sit-down restaurant. Servers in Europe make a paycheck and tips are considered a small "bonus" — to reward great service, or to simply round the total bill to a convenient number. In most countries, 5 to 10 percent is adequate and 15 or 20 percent is unheard of.