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 $48.39   13.686%   $55.0127   $55.01   $55.00   $55.00  
  Purchase #2 $153.53   3.676%   $159.1738   $159.17   $159.15   $159.20  
  Purchase #3 $177.47   5.574%   $187.3622   $187.36   $187.35   $187.40  
  Purchase #4 $185.60   11.312%   $206.5951   $206.60   $206.60   $206.60  
  Purchase #5 $209.53   8.857%   $228.0881   $228.09   $228.10   $228.10  
  Purchase #6 $112.81   11.650%   $125.9524   $125.95   $125.95   $126.00  
  Purchase #7 $240.62   6.228%   $255.6058   $255.61   $255.60   $255.60  
  7 purchase totals = $1,127.95       $1,217.7901   $1,217.79   $1,217.75   $1,217.90