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 $209.51   8.709%   $227.7562   $227.76   $227.75   $227.80  
  Purchase #2 $198.60   9.744%   $217.9516   $217.95   $217.95   $218.00  
  Purchase #3 $239.35   9.103%   $261.138   $261.14   $261.15   $261.10  
  Purchase #4 $202.54   9.581%   $221.9454   $221.95   $221.95   $221.90  
  Purchase #5 $85.71   8.629%   $93.1059   $93.11   $93.10   $93.10  
  Purchase #6 $64.59   10.269%   $71.2227   $71.22   $71.20   $71.20  
  Purchase #7 $154.99   9.183%   $169.2227   $169.22   $169.20   $169.20  
  7 purchase totals = $1,155.29       $1,262.3425   $1,262.35   $1,262.30   $1,262.30