How do you deal with the interviews?

How do you deal with the interviews? I am currently hired as a cashier (even the manager didn't believe I was the right person for the job, but they reaaally needed cashiers for the winter holidays). It's okay, I repeat so much the "Hello/have a good day/ the total sum is..." it became my second nature, but, I want more of a back office job? I applied, I was called for the interviews, then they noticed my stutter and everything just go downhill. They of course don't comment on it, but they don't hire me either. So, how you did you get hired as a stutter?