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 $117.96   13.533%   $133.9235   $133.92   $133.90   $133.90  
  Purchase #2 $94.84   4.277%   $98.8963   $98.90   $98.90   $98.90  
  Purchase #3 $46.84   5.186%   $49.2691   $49.27   $49.25   $49.30  
  Purchase #4 $55.94   11.474%   $62.3586   $62.36   $62.35   $62.40  
  Purchase #5 $245.88   6.544%   $261.9704   $261.97   $261.95   $262.00  
  Purchase #6 $24.90   10.477%   $27.5088   $27.51   $27.50   $27.50  
  Purchase #7 $178.45   6.600%   $190.2277   $190.23   $190.25   $190.20  
  7 purchase totals = $764.81       $824.1544   $824.16   $824.10   $824.20