Should I mention my clinical rotations in my nursing cover letter for new grad positions?

If your school allowed/required you to do a Capstone Clincal placement during your last semester you should mention it if you are applying to work in that area. It's useful to indicate any focused experience in a specialty that you are applying to work in.

It doesn’t hurt. Most new grads don’t have much else to put on their resume! Highlight the areas you were oriented!