I once accidentally threw our mops in an industrial bin and I still haven't told my boss
How come you have not told your boss yet?
He gets angry every time someone does that. I was thinking he is going to scold me once he finds out about it.
You need to own up to your boss. Lying about it is worse than doing it in the first place.
Ok, I will tell him now.
Just know that he will be angry with you and try to remember to not throw away the mops. Being honest with him is the best policy.