Let me begin by saying that I have a lot of respect for people who work "fast-food" with even a moderate level of competence. I could not do it. I daresay I'd go "postal" within about the first 15 minutes.
Had one very similar to Marty's last post. Went to a Taco Bell last year, ordered $4.68 of stuff. Paid with a $10. Counter person discovers that he doesn't have enough change, will have to get the manager to get some out of the safe. After about 5 minutes the manager figures out there ISN'T any change in the safe, only big bills. SO, the manager leaves the store to go to the bank to get change.
I say, "no problem, I can dig out the exact change"; (which I do), "give me back my $10 and I'll give you the exact change". Counter Person says, "Oh, No, I can't do that, I already entered the $10 in the register, and I can't change that without a manager over-ride". And, of course, the manager is on the way to the bank, so he is not there to do an override. "Besides, I wouldn't know how much change to give you without the register telling me". "How would I know that you aren't trying to cheat me? I have to pay for any shortage from my register out of my own pocket."
I say: "Exact change. My order is $4.68, I give you $4.68 for the food, you give me back the $10 bill that you can't change and we are even."
He says: "But how do I know that? I can only do what the register tells me to do, and I am NOT going to pay out of my pocket if I come up short."
I just left before my head exploded with frustration. Taco Bell, you owe me ten bucks.