I can't believe I reported real money as fake money in the cash register.
I can't believe it either. Why would you lie about the money?
My job wasn't giving me enough money so I'm taking the money I claimed was fake and taking it for myself.
If the money was real, you should be honest with your employer. If you lie to them and take the money, you are putting your job at risk. If they find out you lied and stole the money, you will certainly be fired and probably be reported to the police.
Man, nothing bad is going to happen from me taking this money.
You would be surprised. They probably have cameras there and will see that it was real money. And by being dishonest with your employer, you might get a bad review and have trouble getting another job after you get fired from this one.