But why do you assert largest to smallest is the wrong way (other than what the girl at Pak'n'Save said)? "18.30 and 1 makes 19.30, and 50c makes 19.80, and 20c makes 20.00" makes at least as much sense doesn't it?
Only if you have already worked out in advance what the change should be. If you are doing it manually "on the fly" (admittedly I'm old and first learned to give change in pounds, shillings and pence) and need to get to the next highest denomination as you go, then smallest to largest is only the way to go.
All POS computers will work that out for the staff. Only problem is when they see you holding a $50 or a $100 so push that in before telling you the amount and you decide to add a little more in coins to get whole notes back as change instead of shrapnel.
I believe counting out the change is for the benefit of the customer, not the staff.