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 $241.39   8.277%   $261.3699   $261.37   $261.35   $261.40  
  Purchase #2 $104.44   9.630%   $114.4976   $114.50   $114.50   $114.50  
  Purchase #3 $215.49   6.172%   $228.79   $228.79   $228.80   $228.80  
  Purchase #4 $139.48   12.634%   $157.1019   $157.10   $157.10   $157.10  
  Purchase #5 $43.84   4.289%   $45.7203   $45.72   $45.70   $45.70  
  Purchase #6 $217.66   10.403%   $240.3032   $240.30   $240.30   $240.30  
  Purchase #7 $221.65   8.372%   $240.2065   $240.21   $240.20   $240.20  
  7 purchase totals = $1,183.95       $1,287.9894   $1,287.99   $1,287.95   $1,288.00