Should I use rel="nofollow" for the links that add products to my cart ?

This rel is usually used to specify user posts. Therefore, will google think that my site is a blog because there are so many rel="nofollow" all over my site ?

Is there a special rel or some other method for this kind of link? (I'm using html5).

(I really want to use a text link rather than an image link or a form button.)

<a href="path-to-my-cart.php?id=12345" rel="nofollow">Add to Cart</a>

This rel is usually used to specify user posts.

No it is not.

rel="nofollow" is an attribute that is used to indicate to Search Engines that you do not trust or vouch for that particular link.