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 $68.28   11.674%   $76.251   $76.25   $76.25   $76.30  
  Purchase #2 $17.87   8.544%   $19.3968   $19.40   $19.40   $19.40  
  Purchase #3 $158.39   4.555%   $165.6047   $165.60   $165.60   $165.60  
  Purchase #4 $81.72   8.462%   $88.6351   $88.64   $88.65   $88.60  
  Purchase #5 $73.81   6.664%   $78.7287   $78.73   $78.75   $78.70  
  Purchase #6 $247.47   5.394%   $260.8185   $260.82   $260.80   $260.80  
  Purchase #7 $30.42   4.388%   $31.7548   $31.75   $31.75   $31.80  
  7 purchase totals = $677.96       $721.1896   $721.19   $721.20   $721.20