That's why you count down the register beforehand. And after that its your responsibility to watch it. Harsh life lesson in retail. But if you think it was a co-worker, narrow down a list of suspects and take note.
That's what I did tho, I counted the money and all of that before I handed it in and I gave correct change, contrary to what the people who liked your comment think. I don't steal money either, why steal money when I have my own??