The explanation from the land of Frobozz certainly clears up what you were getting at. I would posit, though, that most countries, unlike Frobozz, have designed their currency structure along some sort of logic which would limit this possiblity.

Humans regularily give change from a machine displaying only a single total, without benefit of a breakdown, moving from one bin to the next, trying to make a good total. There is little "wiggle room" in a fully stocked register. It is only when they start to run out of things that it gets interesting.

I, for one, would not want to design a Frobozzian register which had to explain how to give change.

The absence of a "penny" placeholder would cause a little havoc with change dispensing from a mechanical perspective, as you pointed out with your $0.30 example, which would be rendered impractical.