What is the event fires when change the grand total in cart?

Question

I want to write an observer function which will fire whenever the cart total is changing.

Eg: When add/remove products in the cart, 
Add rewards/coupon codes to the cart

My observer function will check whether the cart grand total is greater than zero. If not it will do some calculation with the grand total and save that calculated value to the quote.

I have tried the following events. But non of them fulfilled the requirement.

    controller_action_postdispatch_checkout_cart_index
sales_quote_address_collect_totals_before

Any suggestions will be appreciated. Thanks in advance.

Answer 1

The following event did the trick.

controller_action_predispatch_checkout_cart_index