@Animal, I understand perfectly how it can feel, but I do think you're overthinking it as well. Since you were the one at the tills since the last count, your manager logically has to consider you a suspect, but seeing how quickly she let it go, I hardly think she genuinely suspects you of stealing. I say don't sweat it. Of course, if it comes up again, you should defend your case, but unless it does, I'd say just forget about it.