In the USA, a penny isn't worth very much. So in shops, there is usually a little 'penny tray' or 'penny jar', where you can leave your unwanted pennies ... and also pick up a few if you're a bit short in payment. It's a separate thing to the 'tip' jar. And, I think, an unusual display of generosity.
I think it would be a pretty neat idea to implement in Australia. I know that we have phased out the 1c and 2c coins... but you could pretty much do the same with the 5c pieces. It is almost as if they're not regarded as legal tender anymore - you can't pay your tolls with them, and the train ticket machines won't accept them either.