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 $61.86   7.514%   $66.5082   $66.51   $66.50   $66.50  
  Purchase #2 $132.73   10.450%   $146.6003   $146.60   $146.60   $146.60  
  Purchase #3 $237.65   10.200%   $261.8903   $261.89   $261.90   $261.90  
  Purchase #4 $43.39   7.226%   $46.5254   $46.53   $46.55   $46.50  
  Purchase #5 $237.42   3.658%   $246.1048   $246.10   $246.10   $246.10  
  Purchase #6 $250.56   8.665%   $272.271   $272.27   $272.25   $272.30  
  Purchase #7 $191.92   8.757%   $208.7264   $208.73   $208.75   $208.70  
  7 purchase totals = $1,155.53       $1,248.6264   $1,248.63   $1,248.65   $1,248.60