Worked for same employer for 20 years. Suddenly was terminated for supposedly taking $5 that was supposed to be payment for a beverage but instead was put in tip jar. If this actually happened it was clearly a mistake and not intentional. Not going to risk job for $5.
Your statement ..."if this actually happened" ... it either did .. or it didn't.
Either way... you state you were a 20 year employee and if this was the only right up or disciplinary action taken against you while employed... you might have a case. Over the years length of time on a job has become less important then it was say 10 or 15 years ago. Hopefully there was no video or this was not an ongoing investigation of you.