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 $76.31   7.400%   $81.9569   $81.96   $81.95   $82.00  
  Purchase #2 $248.70   5.321%   $261.9333   $261.93   $261.95   $261.90  
  Purchase #3 $104.91   8.829%   $114.1725   $114.17   $114.15   $114.20  
  Purchase #4 $70.33   11.508%   $78.4236   $78.42   $78.40   $78.40  
  Purchase #5 $15.41   13.355%   $17.468   $17.47   $17.45   $17.50  
  Purchase #6 $158.45   10.167%   $174.5596   $174.56   $174.55   $174.60  
  Purchase #7 $137.90   5.345%   $145.2708   $145.27   $145.25   $145.30  
  7 purchase totals = $812.01       $873.7847   $873.78   $873.70   $873.90