multiply the product prices rather than summing them

[jabba]

Easy question. I need to multiply the product prices instead of summing them. I mean:

NORMAL CART:

Product 1 = 10$
Prdouct 2 = 20$

Total = 30$

MODIFIED CART:

Product 1 = 10$
Product 2 = 20$

TOTAL = 200$

Is this possible? How? In wich file the cart total is defined? And how to pass it to the checkout function?

Thank you