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 $93.38   9.179%   $101.9514   $101.95   $101.95   $102.00  
  Purchase #2 $11.44   10.197%   $12.6065   $12.61   $12.60   $12.60  
  Purchase #3 $18.63   11.290%   $20.7333   $20.73   $20.75   $20.70  
  Purchase #4 $207.48   12.382%   $233.1702   $233.17   $233.15   $233.20  
  Purchase #5 $107.57   6.295%   $114.3415   $114.34   $114.35   $114.30  
  Purchase #6 $217.94   9.293%   $238.1932   $238.19   $238.20   $238.20  
  Purchase #7 $195.54   5.422%   $206.1422   $206.14   $206.15   $206.10  
  7 purchase totals = $851.98       $927.1383   $927.13   $927.15   $927.10