Used to be the cashier would count back your change.
Next time, I'm using cash and adding a few extra coins and watch the implosion.
I do this all the time, not to confuse the little darlings, but because I don’t want a pocket full of change
If an item costs $19.05 for example, I will give the cashier a 20 and a nickel. Nine times out of nine they slide the nickel back and say I don’t need that. Then the stupidity grows from there.