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 $220.29   8.870%   $239.8297   $239.83   $239.85   $239.80  
  Purchase #2 $102.37   11.622%   $114.2674   $114.27   $114.25   $114.30  
  Purchase #3 $60.90   5.408%   $64.1935   $64.19   $64.20   $64.20  
  Purchase #4 $6.48   3.600%   $6.7133   $6.71   $6.70   $6.70  
  Purchase #5 $47.82   11.768%   $53.4475   $53.45   $53.45   $53.40  
  Purchase #6 $145.76   8.249%   $157.7837   $157.78   $157.80   $157.80  
  Purchase #7 $234.70   11.334%   $261.3009   $261.30   $261.30   $261.30  
  7 purchase totals = $818.32       $897.5360   $897.53   $897.55   $897.50