How do I configure shipping charges as a percentage of the total sale?
You cannot configure a straight percentage method for charging shipping costs, but you can use the Shipping by Currency method to come very close. On the Shipping by Currency screen, set the From and To fields for each row to be $10 or $20 apart (there are 20 rows that you can define, so youll need to determine what values to use to cover all possible order totals). Then set the rates for each shipping method to an amount equal to the desired percentage for that price range.