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 $146.56   10.293%   $161.6454   $161.65   $161.65   $161.60  
  Purchase #2 $78.81   3.211%   $81.3406   $81.34   $81.35   $81.30  
  Purchase #3 $240.58   3.243%   $248.382   $248.38   $248.40   $248.40  
  Purchase #4 $10.69   5.552%   $11.2835   $11.28   $11.30   $11.30  
  Purchase #5 $68.35   11.651%   $76.3135   $76.31   $76.30   $76.30  
  Purchase #6 $122.44   8.830%   $133.2515   $133.25   $133.25   $133.30  
  Purchase #7 $233.58   11.760%   $261.049   $261.05   $261.05   $261.00  
  7 purchase totals = $901.01       $973.2655   $973.26   $973.30   $973.20