This PDF document is provided by Rice University and was created using information from two chemistry education websites. It provides a more detailed description of the various rules and usage of significant figures.
This source is provided by Purdue University and contains information regarding addition & subtraction, multiplication & division, rounding off, and determining the number of significant figures.
Created by a chemistry faculty member at the University of South Carolina, this link will walk you through a quick tutorial on the usage of significant figures.