How should I dress for a 3rd round interview over coffee?

I have a third round interview this week at a local upscale coffee shop. My first interview was over the phone and the second in their office. I wore a suit to the 2nd interview, but since this one is over coffee, I"m not sure what to do. Part of the interview is to determine whether or not I would work well with my future supervisor, so that makes me think I could dress a little more causally. Would a nice pencil skirt and blouse be okay for this round? I am a young-ish female applying for a job in a small, relatively new company.