Germany
W/W: very normal to not tip, but some will leave a few coins from their change or round up to the next Euro (or two)
This is not correct. The information appears to be coming from tourists who "heard" that this is what you do.
Don't do this except in student hangouts or if you don't plan to ever come back. The waiters normally don't complain, maybe that's what confuses the tourists.
I normally leave an extra 10%. EUR 45 becomes EUR 50 as an example. Everybody I know does this as well. More for exceptional service. And I'm not a tourist, I live here.
PS: leave small change might have been true 30 years ago, but not today.