Re: Please explain
Getting physical access to a drawer is not a problem usually anyway, most have a small hole a bit like CD drawers used to have poke a pin in and it releases the lock.
The problem is a cashier would have a discrepancy that would show up on a Z-reading (don't know if they still call it that, acted as tech support for POS software many many years ago), which shows the total from the transactions.
If a cashier was going to fiddle a cash drawer then the ability to do mental arithmetic and keeping the running total in your head for the till, plus what change you should be giving (basically you balance the books in your head), is easier you ring up as no sales (to pop the drawer but no value entered in the checkouts final total), the average customer doesn't care about a receipt.
Depending on the set up, changing prices would not be easy either a lot of the stores had price files sent down to the back office that was then loaded down to the tills, not sure if you could change them after that easily.
It really depends on how they set up their POS network - some stores checkout die completely with loss of the server, some we worked with were pretty robust (and running all on DOS) and would continue because they stored local copies.
I would have though the grand prize was access to the CC merchant services that will be running somewhere the last one I saw (again years ago) used to have a service running on a SCO box and would squirt all that data to a bank that processed it and sent back auth codes for the cards.
I can tell you also many stores do not check when someone turns up looking like they should be working there, I have walked right up to the server racks in the offices of some large chains and not once has someone said anything (I was actually supposed to be doing so btw), ask for where the sign in book is and you are pretty much accepted.