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 $236.98   10.543%   $261.9648   $261.96   $261.95   $262.00  
  Purchase #2 $62.42   11.265%   $69.4516   $69.45   $69.45   $69.50  
  Purchase #3 $19.26   3.680%   $19.9688   $19.97   $19.95   $20.00  
  Purchase #4 $32.54   5.141%   $34.2129   $34.21   $34.20   $34.20  
  Purchase #5 $221.44   7.312%   $237.6317   $237.63   $237.65   $237.60  
  Purchase #6 $250.26   10.617%   $276.8301   $276.83   $276.85   $276.80  
  Purchase #7 $122.68   13.437%   $139.1645   $139.16   $139.15   $139.20  
  7 purchase totals = $945.58       $1,039.2244   $1,039.21   $1,039.20   $1,039.30