Depends on the stores. I work at Justice and you can wear dressy casual to the interview. One guy tried to wear a suit to the interview, but the manager was literally like, "You know, you can just wear jeans." lol. If you're applying for a position at a more upscale place like White House Black Market or Cache or something, an outfit like what Chrissy posted is appropriate. You can pick up some slacks at Walmart for $20 and ballet flats at Walmart or Target for another $10-15. You need dressy clothes for situations like this anyways.

Don't over-prepare. I know that sounds wrong but if you try to rehearse answers or anticipate everything they may ask you, you will drive yourself crazy and they may not even ask you what you planned for.