Rules in Rounding off Significant Figures?

Makes no difference what you are doing. Usually I round to 2 decimal places or 3 sf. Sometimes in physics they say round to the least number of significant figures used in your equation or 3 sf in chem but that's about it. To round to 3 sf, find the highest digit ( eg the 3 in the number 389.564789) and use that as well as the next 2 digits. To round, if the number after your last digit is 5 or higher, add 1 to your last digit. If the number after your last digit is 4 or less, do not change your number. Note that in decimal numbers eg0.0006549, do not include the 0s as your sf unless they are between eg in the number .009054, this rounds to .00905 for 3 sf