I want to add a custom value, i.e custom fees, in the cart page below subtotal, so the Grand total should contain the custom fee. Here i mean to say that during quote-state, the grand total should contain the custom fee. And from the quote- to order-state, the grand total must contain that custom fee.
What you need to do is add a custom "total" entry that will be added to the grand total.
This guide will get you started.