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 $91.53   5.131%   $96.2264   $96.23   $96.25   $96.20  
  Purchase #2 $129.37   8.683%   $140.6032   $140.60   $140.60   $140.60  
  Purchase #3 $243.33   10.538%   $268.9721   $268.97   $268.95   $269.00  
  Purchase #4 $45.32   11.195%   $50.3936   $50.39   $50.40   $50.40  
  Purchase #5 $183.76   13.334%   $208.2626   $208.26   $208.25   $208.30  
  Purchase #6 $25.48   4.786%   $26.6995   $26.70   $26.70   $26.70  
  Purchase #7 $140.53   3.242%   $145.086   $145.09   $145.10   $145.10  
  7 purchase totals = $859.32       $936.2434   $936.24   $936.25   $936.30