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 $65.76   11.530%   $73.3421   $73.34   $73.35   $73.30  
  Purchase #2 $34.33   5.162%   $36.1021   $36.10   $36.10   $36.10  
  Purchase #3 $236.88   3.404%   $244.9434   $244.94   $244.95   $244.90  
  Purchase #4 $248.39   5.360%   $261.7037   $261.70   $261.70   $261.70  
  Purchase #5 $221.95   10.533%   $245.328   $245.33   $245.35   $245.30  
  Purchase #6 $5.66   5.357%   $5.9632   $5.96   $5.95   $6.00  
  Purchase #7 $11.92   13.149%   $13.4874   $13.49   $13.50   $13.50  
  7 purchase totals = $824.89       $880.8699   $880.86   $880.90   $880.80