Would I go to jail for making a mistake at a cash register at work? ?

Nope... Unless the money ( and a lot of that ) is going towards you.

You would not go to jail for making an honest mistake on a cash register. However, if you miss-rang sales for friends and/or pocketed funds from the register they've probably got video surveillance tape to show this and would have you arrested and prosecuted. 

If it's fraud you may end up in jail, but if it is an honest mistake you can pay back the difference and be back at work the very same day or quit after you have paid your boss back the money you lost in the transaction.

Depends on the "mistake" your referring to.

The amount and frequency of discrepancy is a factor. 

IMO that seems very unlikely but doing the walk of shame out the door by Loss Prevention is very awful to anyone who has a conscience. 

If one is not guilty they should be able to plead their case regardless of eloquence. 

I'm very bad at math and have constantly dealt with customers that have last-second offer offsetting change to solidify a dollar...

I think intent should be a consideration - unless one is under scrutiny for other reasons. 

Only if you are being accused of theft by your boss and convicted by a court. Even then, it would have to be  for a substantial amount. 

NO. Depending on the amount, and how often, you may be fired.

In order to come close to the burden of proof for a criminal conviction, it absolutely will NOT be a mistake.

It's possible. 

For it to be theft, there has to be intent, so if it was a mistake, it's not theft, but that doesn't mean that your employer won't believe it was and won't be able to provide the police enough probable cause that it was theft, the money being missing itself being enough probable cause because money in and of itself provides motive. 

You also have to consider that your employer may be convinced it was more than a mistake and report it as theft. Since theft of money provides its own motive, an arrest would then become likely. That's jail. So, yes, you can go to jail, at least until you're arraigned, at which point the charges could be dropped, you could be set free pending trial on your own recognizance, or you could have bail set, which would result in you return to jail until bail was paid. Making bail, you will be free until you're trial or until charges are dropped. 

So, if the police believe you that it was just a mistake, you won't go to jail, but if the police believe you may have stolen it, which will largely rest on what your employer believes, and the police find enough probable cause, which they will if the money is truly missing, then you'll be arrested. Arrested means you will go to jail. That doesn't mean you've been convicted of a crime, but it means that they will hold you in jail until a prosecutor either decides to drop the charges for lack of evidence or arraigns you before a judge.

Even if the prosecutor were to believe it was a mistake, if that prosecutor is extremely zealous, that prosecutor could choose to charge you with and prosecute you for criminal negligence in fulfilling your fiduciary duty as an employee, a legal duty employees have to protect the financial interests of their employer. Such prosecutions are more typical for major financial losses, more than what generally can be lost by a mistake at a cash register, but it is nevertheless a legal possibility. Anyway, if you get such a prosecutor, you are going to be in jail at least until you are arraigned.

If or when you are arraigned and the case goes to trial, like I said, a prosecutor would have to prove that it wasn't just a mistake in order to convict you on theft, prove that the money going missing was an intentional act. Maybe even the prosecutor has footage supplied by the store of you making the mistake, giving that customer a $100 bill instead of a $1 bill or whatever. If the prosecutor can convince a jury beyond reasonable doubt that you did it on purpose, that you're guilty, then the jury will convict you. If convicted, you may go back to jail, or you may get probation or a suspended sentence. 

Maybe you're innocent, but innocent people get convicted about 10% of the time.

no they take the difference out of your paycheck. good incentive for cashiers to make sure they get the till correct.

You tell your supervisor what happened to the best of your ability.