I don't see any way this could be innocent. In this situation, you are either making change correctly or you are holding back money that does not belong to you, where you is our hypothetical server.
Thrust a receipt and a bunch of bills into my hand and vanish before I can even see what I have, which is what happened both times, and suddenly it is a huge inconvenience for me to track you, HS, down, demand you give me what you owe me, with no choice but allowing you to take lots of time and fumble around doing that, while my whole party and I are standing around waiting. No, not innocent, and no way it could be. I am supposed to, in HS's mind, forget about it because it "is too little to worry about." Somehow, hypothetical server thinks it is Ok to short change people as long as it is coins, because it is too much trouble for the patrons to get their actual money back -- and HS will make that so -- and "they're going to tip anyway." It isn't. And I won't, in that circumstance, ever again.