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 $67.79   11.500%   $75.5859   $75.59   $75.60   $75.60  
  Purchase #2 $17.31   5.849%   $18.3225   $18.32   $18.30   $18.30  
  Purchase #3 $175.69   13.765%   $199.8737   $199.87   $199.85   $199.90  
  Purchase #4 $199.38   13.341%   $225.9793   $225.98   $226.00   $226.00  
  Purchase #5 $185.67   13.196%   $210.171   $210.17   $210.15   $210.20  
  Purchase #6 $59.71   4.302%   $62.2787   $62.28   $62.30   $62.30  
  Purchase #7 $163.53   11.741%   $182.7301   $182.73   $182.75   $182.70  
  7 purchase totals = $869.08       $974.9412   $974.94   $974.95   $975.00