When I was in high school my German teacher taught us to tip by default by rounding up and paying with exact change. Is that still a thing when everyone is paying with card?
Let's say the bill says someting between 67€ - 72€, I would round that up to 80€.
Or sometimes (not every time though) when I'm getting a Döner kebab and it's ~7.50€ I'll round that up to the next full €.
Paying in cash is still common at German restaurants though.