How to save two transaction in my shopping cart - php

Question

i have two transaction on my cart.
while i click checkout, why $grand total only one inserted to my db.
and when i echo $grand, it appear two total.
this is my function
function cart(){
$username = $_SESSION['UserID'];
$cart = array();
$sql = mysql_query("SELECT * FROM cart WHERE Username='$username'");
while ($r=mysql_fetch_array($sql)) {
$cart[] = $r;
}
return $cart;
}
this is my process code
for ($i = 0; $i < $j; $i++){
echo $start= $cart[$i]['City_Saler'];
echo $end= $cart[$i]['City_Cust'];
$price= $cart[$i]['Price'];
$gram= $cart[$i]['gram'] / 1000;
echo $kg= ceil($gram);
$query= mysql_query("select * FROM service WHERE Start_Destination='$start' AND End_Destination='$end'");
while($query_row = mysql_fetch_assoc($query)){
$grand=$query_row['ServPriceKG'] + $price ;
}
}
for ($i = 0; $i < $j; $i++){
mysql_query("INSERT INTO ordering_detail(ID_Transaction, ID_Product, User_ID, Service_Name, Service_Package, Qty, gram, Price, Receiver_Name, Receiver_City, Receiver_Subdis, Receiver_Address, Receiver_Prov, Receiver_Phone, Grandtotal, Payment, Stat_Transfer_Item, ID_Saler)
VALUES('$idtransaction', '{$cart[$i]['ID_Product']}', '$cusid', '$service', '$paket', '{$cart[$i]['qty']}', '$kg', '{$cart[$i]['Price']}', '$name', '$reci', '$subdis', '$address', '$prov', '$phone', '$grand', '-', '-', '{$cart[$i]['ID_Saler']}')");
}
mysql_query("DELETE FROM preview_ordering WHERE ID_Preview= '$id'");
for ($i = 0; $i < $j; $i++) { mysql_query("DELETE FROM cart WHERE ID = {$cart[$i]['ID']}");}
header('Location:cart.php');
please help me out