How to price your book?

This is a question for those who have their books on amazon, kindle, goodbook and other publishing websites.

I've not published my book outside of RR as it's not finished, but I am curious on the matter regardless. I've seen many different books on those sites and they all have varying prices. So, how do you decide you want your book to be 5$ and not 10.99$?

Is it even something the author decides or is it decided by the publisher?