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 $234.83   11.548%   $261.9482   $261.95   $261.95   $261.90  
  Purchase #2 $71.65   4.457%   $74.8434   $74.84   $74.85   $74.80  
  Purchase #3 $151.97   3.581%   $157.412   $157.41   $157.40   $157.40  
  Purchase #4 $51.66   11.230%   $57.4614   $57.46   $57.45   $57.50  
  Purchase #5 $112.87   4.374%   $117.8069   $117.81   $117.80   $117.80  
  Purchase #6 $103.66   6.720%   $110.626   $110.63   $110.65   $110.60  
  Purchase #7 $115.86   10.177%   $127.6511   $127.65   $127.65   $127.70  
  7 purchase totals = $842.50       $907.7490   $907.75   $907.75   $907.70