If convicted, how long would someone go to jail for theft/fraud in Portland Oregon for stealing from atm machine at work? (bar)?

It is not possible to give you a specific answer to this question, because there are too many variables. I can tell you that you should absolutely retain the services of a lawyer at once, and make no statements to the police, your employer, or anyone else (including on-line services) until you have that lawyer's advice.

Depending on how much money was taken and the attendant circumstances, your charge could range from misdemeanor to felony and result in a little bit of probation and repayment of the fine, to prison time.