You'd get penalised for excessive rounding. So long as you get the right answer to 4 or 5 SF, you'll be fine. If you're using values from the Tables in your calculations, then use all the number given in the Tables, and you can't lose out. If you're using your calculator to calculate values, my advice is to use the memory function to store intermediate values (so you have no loss of accuracy) and then round your final answer to 4 or 5 SF, whatever appears sensible.
