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 $66.32   13.537%   $75.2977   $75.30   $75.30   $75.30  
  Purchase #2 $130.49   3.616%   $135.2085   $135.21   $135.20   $135.20  
  Purchase #3 $112.39   8.433%   $121.8678   $121.87   $121.85   $121.90  
  Purchase #4 $71.84   13.141%   $81.2805   $81.28   $81.30   $81.30  
  Purchase #5 $126.77   3.831%   $131.6266   $131.63   $131.65   $131.60  
  Purchase #6 $181.93   3.852%   $188.9379   $188.94   $188.95   $188.90  
  Purchase #7 $237.76   10.178%   $261.9592   $261.96   $261.95   $262.00  
  7 purchase totals = $927.50       $996.1782   $996.19   $996.20   $996.20