Being an American I’ve learned the standard for tipping is 20%. But outside of America that differs greatly. For instance, in Italy for a very long time it was customary not to tip. When you pay the servizio (service charge) and/or the coperto (cover charge), (which if it is listed at the restaurant it is mandatory to pay) you don’t have to leave a tip on top of that charge. I’ve seen many people avoid going into a place because of the service or cover charge, but knowing that those charges would be considered all you needed to leave, would you still avoid them? Many times I’ve seen the charge at 2.50 Euros per person. So by American standards 2.50 would be 20% of a 12.50 bill. How often do you spend only 12.50 at dinner? You’re actually getting a bargain at 2.50.
Italians will at times round up a bill to not wait for change, as service in Italy is not as quick is if you go into an American Ruby Tuesday’s or TGI Fridays (what’s with all the American restaurants being named after days of the week?), etc which is all about turning tables quickly and making those tips. So, if you want to get out of there tell your server to keep the change. (In Italian this translates to “tenga il resto”.)
If you have really great service, leave a tip if you choose, as it is appreciated. But again tipping in general, especially for things like a coffee, is not a regular thing in Italy. At least for Americans it is a hard habit to break so know that tipping when done is generally 10% of your bill minus the cover or service charge you paid.
NOTE: In my travels I have begun to see that in big tourist cities such as Rome, Florence, Milan, Venice etc, the Italians have gotten used to receiving tips from the tourists and may actual expect them, so leave a couple coins if you feel obliged.