problem with store cart details and summary

i put the code the page the user is finish the checkout, but the code kill all sesions less de sessio ID for the ordersummary, that still the same...and the user try to buy again the second order he buys kill the first order details table. I don´t know why still make that...i copy and paste just like that :

<?php
// Initialize the session.
// If you are using session_name("something"), don't forget it now!
session_start();

// Unset all of the session variables.
$_SESSION = array();

// If it's desired to kill the session, also delete the session cookie.
// Note: This will destroy the session, and not just the session data!
if (ini_get("session.use_cookies")) {
$params = session_get_cookie_params();
setcookie(session_name(), '', time() - 42000,
$params["path"], $params["domain"],
$params["secure"], $params["httponly"]
);
}

// Finally, destroy the session.
session_destroy();
?>

I have to put something else?.....