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 $240.53   8.520%   $261.0232   $261.02   $261.00   $261.00  
  Purchase #2 $235.58   7.803%   $253.9623   $253.96   $253.95   $254.00  
  Purchase #3 $71.76   8.853%   $78.1129   $78.11   $78.10   $78.10  
  Purchase #4 $73.41   10.667%   $81.2406   $81.24   $81.25   $81.20  
  Purchase #5 $195.33   13.283%   $221.2757   $221.28   $221.30   $221.30  
  Purchase #6 $46.44   9.584%   $50.8908   $50.89   $50.90   $50.90  
  Purchase #7 $15.63   5.763%   $16.5308   $16.53   $16.55   $16.50  
  7 purchase totals = $878.68       $963.0363   $963.03   $963.05   $963.00