Q: Should i use rel=”nofollow” for my internal links?
In general:NO! and if you are linking one page from on you site to another page on you site you should not use nofollow tag.
There is been all this page sculpting techinques and it used to work,  nut now it as myth.
But in theory, you could use rel=”nofollow” for your login, register or shopping cart pages, because Google and any other Search Engines they dont’ know how to register or use a credit card.
However, if you are linking out to  3rd party …