Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $129.40   10.720%   $143.2717   $143.27   $143.25   $143.30  
  Purchase #2 $91.80   9.238%   $100.2805   $100.28   $100.30   $100.30  
  Purchase #3 $231.53   12.739%   $261.0246   $261.02   $261.00   $261.00  
  Purchase #4 $190.29   13.485%   $215.9506   $215.95   $215.95   $216.00  
  Purchase #5 $30.92   5.794%   $32.7115   $32.71   $32.70   $32.70  
  Purchase #6 $89.41   6.215%   $94.9668   $94.97   $94.95   $95.00  
  Purchase #7 $63.26   11.413%   $70.4799   $70.48   $70.50   $70.50  
  7 purchase totals = $826.61       $918.6856   $918.68   $918.65   $918.80