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 $76.97   9.655%   $84.4015   $84.40   $84.40   $84.40  
  Purchase #2 $172.89   12.872%   $195.1444   $195.14   $195.15   $195.10  
  Purchase #3 $185.26   5.556%   $195.553   $195.55   $195.55   $195.60  
  Purchase #4 $189.61   4.775%   $198.6639   $198.66   $198.65   $198.70  
  Purchase #5 $239.31   9.247%   $261.439   $261.44   $261.45   $261.40  
  Purchase #6 $164.66   13.240%   $186.461   $186.46   $186.45   $186.50  
  Purchase #7 $132.47   6.135%   $140.597   $140.60   $140.60   $140.60  
  7 purchase totals = $1,161.17       $1,262.2598   $1,262.25   $1,262.25   $1,262.30