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 $118.47   6.262%   $125.8886   $125.89   $125.90   $125.90  
  Purchase #2 $240.95   8.614%   $261.7054   $261.71   $261.70   $261.70  
  Purchase #3 $92.91   13.813%   $105.7437   $105.74   $105.75   $105.70  
  Purchase #4 $164.34   6.756%   $175.4428   $175.44   $175.45   $175.40  
  Purchase #5 $41.27   11.261%   $45.9174   $45.92   $45.90   $45.90  
  Purchase #6 $66.46   5.671%   $70.2289   $70.23   $70.25   $70.20  
  Purchase #7 $8.82   5.703%   $9.323   $9.32   $9.30   $9.30  
  7 purchase totals = $733.22       $794.2498   $794.25   $794.25   $794.10