When I was working minimum wage at a gas station many eons ago, we would have '2 for $x' specials where x is less than 2 times the individual price of whatever item.
People would often not want to buy 2, but I would ring up 2 in the till for the special price and charge them for the single. Then when the next person did the same, I would charge them for the other single.
So over the day, I would sell 10 energy drinks at say $4, but ring them up as 5 '2 for $6' specials. This would put the till up by $10, and then I would use that $10 to have a free meal.
When I worked at the window of a national pizza chain, if you paid in cash and told me to "keep the change," I'd mark your order as cancelled and pocket the whole bill.
I still feel shitty about it but I was making $7/hr as a college student and it sure beat my AM selling pressed pills from the backdoor after close