In Canada, it's nearly universal that the debit card system prints out two copies of the debit receipt. One copy goes in the till. If there's any discrepancy, then they can check the paper copies. Otherwise, just file them for 90 days, then shred.
So that raises the question of how do you cope with patrons who possess neither debit, nor credit cards? HCC had a booth where you could purchase a card that carried a certain amount of credit, but that was outside the regular banking systems. It's probably here that the skimming took place, but only time will tell. Maybe... I'm not holding my breath.