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 $51.86   6.524%   $55.2433   $55.24   $55.25   $55.20  
  Purchase #2 $32.62   9.316%   $35.6589   $35.66   $35.65   $35.70  
  Purchase #3 $124.86   6.750%   $133.2881   $133.29   $133.30   $133.30  
  Purchase #4 $188.35   3.156%   $194.2943   $194.29   $194.30   $194.30  
  Purchase #5 $146.95   11.193%   $163.3981   $163.40   $163.40   $163.40  
  Purchase #6 $183.84   6.730%   $196.2124   $196.21   $196.20   $196.20  
  Purchase #7 $233.66   11.770%   $261.1618   $261.16   $261.15   $261.20  
  7 purchase totals = $962.14       $1,039.2569   $1,039.25   $1,039.25   $1,039.30