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 $44.96   11.234%   $50.0108   $50.01   $50.00   $50.00  
  Purchase #2 $39.89   3.438%   $41.2614   $41.26   $41.25   $41.30  
  Purchase #3 $60.45   6.758%   $64.5352   $64.54   $64.55   $64.50  
  Purchase #4 $243.27   7.589%   $261.7318   $261.73   $261.75   $261.70  
  Purchase #5 $112.67   11.797%   $125.9617   $125.96   $125.95   $126.00  
  Purchase #6 $229.54   9.659%   $251.7113   $251.71   $251.70   $251.70  
  Purchase #7 $158.95   3.181%   $164.0062   $164.01   $164.00   $164.00  
  7 purchase totals = $889.73       $959.2184   $959.22   $959.20   $959.20