Students should always quote their final answer to an accuracy consistent with the accuracy of the figures given in the question So, if the numbers you are given to work with are only accurate to 3 sig figs then your answer can't be more accurate, no matter how many decimal places appear on your calculator screen
all digits between and including the first non-zero digit from the left, through the last digit [Bevington, 4] (e g 0 05070 has 4 significant figures )