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 $206.57   9.777%   $226.7663   $226.77   $226.75   $226.80  
  Purchase #2 $53.58   11.302%   $59.6356   $59.64   $59.65   $59.60  
  Purchase #3 $193.34   11.587%   $215.7423   $215.74   $215.75   $215.70  
  Purchase #4 $10.47   10.410%   $11.5599   $11.56   $11.55   $11.60  
  Purchase #5 $116.76   13.137%   $132.0988   $132.10   $132.10   $132.10  
  Purchase #6 $21.71   3.532%   $22.4768   $22.48   $22.50   $22.50  
  Purchase #7 $236.30   10.723%   $261.6384   $261.64   $261.65   $261.60  
  7 purchase totals = $838.73       $929.9181   $929.93   $929.95   $929.90