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 $224.77   12.452%   $252.7584   $252.76   $252.75   $252.80  
  Purchase #2 $192.68   7.550%   $207.2273   $207.23   $207.25   $207.20  
  Purchase #3 $222.37   5.655%   $234.945   $234.95   $234.95   $234.90  
  Purchase #4 $218.38   4.235%   $227.6284   $227.63   $227.65   $227.60  
  Purchase #5 $206.33   9.718%   $226.3811   $226.38   $226.40   $226.40  
  Purchase #6 $41.53   4.854%   $43.5459   $43.55   $43.55   $43.50  
  Purchase #7 $102.61   11.499%   $114.4091   $114.41   $114.40   $114.40  
  7 purchase totals = $1,208.67       $1,306.8952   $1,306.91   $1,306.95   $1,306.80