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 $226.53   9.130%   $247.2122   $247.21   $247.20   $247.20  
  Purchase #2 $101.95   7.334%   $109.427   $109.43   $109.45   $109.40  
  Purchase #3 $106.43   7.496%   $114.408   $114.41   $114.40   $114.40  
  Purchase #4 $127.57   11.239%   $141.9076   $141.91   $141.90   $141.90  
  Purchase #5 $38.78   12.819%   $43.7512   $43.75   $43.75   $43.80  
  Purchase #6 $240.30   8.822%   $261.4993   $261.50   $261.50   $261.50  
  Purchase #7 $41.85   12.186%   $46.9498   $46.95   $46.95   $46.90  
  7 purchase totals = $883.41       $965.1551   $965.16   $965.15   $965.10