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 $38.76   13.383%   $43.9473   $43.95   $43.95   $43.90  
  Purchase #2 $97.86   4.561%   $102.3234   $102.32   $102.30   $102.30  
  Purchase #3 $5.53   11.483%   $6.165   $6.17   $6.15   $6.20  
  Purchase #4 $241.54   8.429%   $261.8994   $261.90   $261.90   $261.90  
  Purchase #5 $101.92   4.350%   $106.3535   $106.35   $106.35   $106.40  
  Purchase #6 $248.50   6.685%   $265.1122   $265.11   $265.10   $265.10  
  Purchase #7 $116.85   10.758%   $129.4207   $129.42   $129.40   $129.40  
  7 purchase totals = $850.96       $915.2215   $915.22   $915.15   $915.20