Math question

I'm working on a little shopping cart script and when I get to the checkout portion I show what is in the cart and for each item I show the quanity, price per unit then I show the total cost for that item. So basically it looks like $total = $qty * $price My question is how do I add the value of $total to give the over total of the order? Since there may be one or more different items in the cart I can't seem to pin down the math that will allow for the changing amount of items in the cart. since there may be just one $total variable or 5. I hope I'm clear enough on this, any ideas or thoughts would be welcome and appreciated. Thanks!