Then what's the problem? You stored float 1.410 and got back float 1.41. They're equal. That's not jQuery, it's javascript: http://jsfiddle.net/kgp2H/1/

Edit, after the parent was edited to include the data attribute example:

You should update your post to clarify that you're talking about data attributes. That's a significant detail and shouldn't have been left out.

Now that you've clarified, jQuery does behave as you've stated, but it's not a bug. I can see how it could be unexpected behavior to some, but it's explicitly stated in the .data() documentation:

  Every attempt is made to convert the string to a 
  JavaScript value (this includes booleans, numbers, 
  objects, arrays, and null) otherwise it is left as a 
  string. To retrieve the value's attribute as a string 
  without any attempt to convert it, use the attr() method.

http://api.jquery.com/data/#data2