$this->cart->total() - Can this be manipulated?

[eluser]EdgeTube[/eluser]
Hi all,

I am trying to create a coupon code function using the shopping cart class. For some reason I cannot manipulate the $this->cart->total() as I am given an error "Can't use method return value in write context."

Any ideas on how I could apply a coupon code and somehow change the total?

Thanks!