Here in Australia, we got rid of our 1c and 2c coins years ago; the way it works is that if you pay for something with cash, 1 and 2 round to 0; 3, 4, 6 and 7 round to 5; 8 and 9 round to 10. It works out pretty well, but since so many people pay for things with credit/debit cards, it doesn't matter much in practice.

Those are the legally suggested rules, but not every company exactly follows them; I recall hearing that one supermarket chain always rounds downward at purchase time, but rounds up if you return the product for some reason - a nice gesture.