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 $87.75   10.182%   $96.6847   $96.68   $96.70   $96.70  
  Purchase #2 $43.73   5.299%   $46.0473   $46.05   $46.05   $46.00  
  Purchase #3 $47.83   9.449%   $52.3495   $52.35   $52.35   $52.30  
  Purchase #4 $170.78   13.576%   $193.9651   $193.97   $193.95   $194.00  
  Purchase #5 $157.40   9.863%   $172.9244   $172.92   $172.90   $172.90  
  Purchase #6 $249.34   4.674%   $260.9942   $260.99   $261.00   $261.00  
  Purchase #7 $132.49   6.619%   $141.2595   $141.26   $141.25   $141.30  
  7 purchase totals = $889.32       $964.2247   $964.22   $964.20   $964.20