They can round down the card transactions too if it’s really a problem to charge differing amounts.

For those that seriously think this would be a major problem there was a comedy skit circulating in Australia when this happened. A guy would push his car to the petrol pump, fill with 2c of petrol, rounded down to 0. The guy at the counter just laughed at it. You could in theory do this 1000 more times (would take hours) for $20 of free petrol. At least until the worker got sick of it and enforced the whole right to refuse service.

> enforced the whole right to refuse service.

This is what everyone forgets. If you can't provide exact change, then you can refuse service.

I had this same idea and seem to recall even trying it, but it was mostly thwarted when they added minimum liquid delivery amounts.