Get the new Total Price value from cart after item added

[LiranMatok]

I made a Free Shipping Calculator that Stick to the head of the website everytime.
Its works nice, but I have a problem.
When I add to cart item, the value that I have update only if I refresh or move to other page - So, I need your help to find how I can update my value live when I add to cart item .
As I see it I need to edit the addToCart func, but I dont know how to.. and how to get the new value at my header-template when the addToCart func at theme.js
Thanks a head.