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 $68.38   10.274%   $75.4054   $75.41   $75.40   $75.40  
  Purchase #2 $171.43   10.871%   $190.0662   $190.07   $190.05   $190.10  
  Purchase #3 $240.80   8.458%   $261.1669   $261.17   $261.15   $261.20  
  Purchase #4 $62.98   4.427%   $65.7681   $65.77   $65.75   $65.80  
  Purchase #5 $194.85   11.545%   $217.3454   $217.35   $217.35   $217.30  
  Purchase #6 $210.30   7.154%   $225.3449   $225.34   $225.35   $225.30  
  Purchase #7 $89.63   8.389%   $97.1491   $97.15   $97.15   $97.10  
  7 purchase totals = $1,038.37       $1,132.2460   $1,132.26   $1,132.20   $1,132.20