I can't say I've ever dealt with managers like that but I did used to work as a cashier and had to deal with customers that pull tricks like that. We used to call that one "the oldest trick in the book". Another variation is where, the customer gets back, say, $15.33 in change, then they start to walk away and pocket the 10 when you aren't looking then turn around and say "oh hey, you only gave me $5.33! Of course, then you apologize, and hand them another 10 dollar bill, only to find your drawer $10 short when you close.
What we always did to avoid stuff like that was count the money in front of the customer, especially if they hand you a large amount, or if they're getting a large amount of change back. That way, they know, that we know how much money is being handed over.