YMMV. I can slip a few bills in with my credit cards. If I can't really just ignore coins like I generally do in the US (not that I use much cash in the US at this point), I need some separate pouch to carry them. I dislike ~$1+ coins because you pretty much have to use them if you're paying and getting change in cash.

$1 coins have flopped whenever they've been tried in more or less living memory in the US.