Are all the posters who are saying "I work at a restaurant, we always round the change" or "Nobody ever wants the coins" or "I never care about the coins" in the US? I'm in Australia, and I've never seen anyone assume that not getting every cent of your change could possibly be OK.
If the server was keeping it, that would be petty theft, and if the restaurant was keeping it, that would be fraud - and either way there would be trouble! The thing about rounding your change to the nearest dollar wouldn't fly, either. We round to the nearest 5c and we have RULES about how you're meant to do it!
I wonder if it's at least partly because we're not a tipping culture here? In places that do tip as a matter of course, perhaps a lot of people feel that you're going to be giving your server some of your change anyway, so it's no big deal to start with the coins?