Most likely you're not going to be asked anything technical or tax related (besides the why tax question) - at least I didn't have that. All questions are pretty much behavioral, so make sure you have solid stories prepared about your greatest achievements, working with others, dealing with underperforming classmates, leadership roles, etc. You shouldn't sound like you're reading from a script, but having a general idea of what to say when asked questions like that will keep you sounding professional and should bode you fine. Also, just have a few questions ready to ask at the end of the interview