I once asked my hostess (Zimmer in a privat Haus)in Germany about tipping in restaurants. I told her how I tipped at the time, and she scolded me for over-tipping. She stated emphatically, that you only round the total up to the nearest euro. The believe the wait staff is paid adequately; it's just petty or impolite to take the small change (whereas, in the US, restaurant expect you to pay their employees).
Well, I can't bring myself to leave a 10 cent tip on a 12,90€ bill, so I add 50 cent and round it up, so I'd leave 14,00€ on a 12,90€ bill. When I'm traveling alone, that amounts to between 5% and 10% . If there are two of us, I often add another euro.
In Europe, you don't leave the tip on the table. When the waiter tells you, or shows you, the total amount, round it up and say, for 12,90€, "vierzehn Euro" (it helps to know a little of the language).