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 $82.53   13.344%   $93.5428   $93.54   $93.55   $93.50  
  Purchase #2 $56.76   10.161%   $62.5274   $62.53   $62.55   $62.50  
  Purchase #3 $33.47   9.758%   $36.736   $36.74   $36.75   $36.70  
  Purchase #4 $71.88   9.307%   $78.5699   $78.57   $78.55   $78.60  
  Purchase #5 $116.34   13.523%   $132.0727   $132.07   $132.05   $132.10  
  Purchase #6 $72.55   12.785%   $81.8255   $81.83   $81.85   $81.80  
  Purchase #7 $118.27   5.818%   $125.1509   $125.15   $125.15   $125.20  
  7 purchase totals = $551.80       $610.4252   $610.43   $610.45   $610.40