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 $64.95   11.794%   $72.6102   $72.61   $72.60   $72.60  
  Purchase #2 $19.98   8.394%   $21.6571   $21.66   $21.65   $21.70  
  Purchase #3 $244.93   6.466%   $260.7672   $260.77   $260.75   $260.80  
  Purchase #4 $245.26   6.514%   $261.2362   $261.24   $261.25   $261.20  
  Purchase #5 $14.37   10.481%   $15.8761   $15.88   $15.90   $15.90  
  Purchase #6 $175.50   11.111%   $194.9998   $195.00   $195.00   $195.00  
  Purchase #7 $100.58   8.560%   $109.1896   $109.19   $109.20   $109.20  
  7 purchase totals = $865.57       $936.3362   $936.35   $936.35   $936.40