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 $221.65   13.758%   $252.1446   $252.14   $252.15   $252.10  
  Purchase #2 $44.45   11.822%   $49.7049   $49.70   $49.70   $49.70  
  Purchase #3 $10.50   5.229%   $11.049   $11.05   $11.05   $11.00  
  Purchase #4 $36.38   13.217%   $41.1883   $41.19   $41.20   $41.20  
  Purchase #5 $248.30   5.400%   $261.7082   $261.71   $261.70   $261.70  
  Purchase #6 $102.26   12.198%   $114.7337   $114.73   $114.75   $114.70  
  Purchase #7 $32.63   11.498%   $36.3818   $36.38   $36.40   $36.40  
  7 purchase totals = $696.17       $766.9105   $766.90   $766.95   $766.80