Frankie got it spot on. She complains on this post about why cashiers always balance the coins on top of the notes before giving it to you when they can give it to you separately. I have to admit I never really thought about it, till after I read that post.
But now I realise how annoying it is everytime it happens as well. Because I will always have this fear that the coins might slid off the bills, drop all over the floor and I end up looking like an clumsy oaf who can't even keep his change properly. And like she mentions, it's a real hassle when you have other things in your hands, then it becomes a real balancing act.
So if you ever worked as a cashier, why do you do that?