NCEES limits the calculator models you may use during the test. A listing can be found here. We suggest that you gain familiarity with your calculator by using it during your preparation. 

Which calculator should you choose? After reviewing the possible candidates, we suggest you choose one of the following models below.  Both feature multi-line displays, are priced economically (the HP 33s and HP35s are $99 and $35 respectively), and provide natural looking representations of fractions. Both are solar powered with a battery back up. If you really want to dive into the details, take a look at the Casio manual and the TI manual.

However, if I had to choose one calculator, it would be the TI-36X Pro. Check out this video to see the calculator in working action.