Paypal Standard won't take the total to paypal portal.

open: catalogincludesmodulespaymentpaypal_standard.php

find:
function process_button() {

below you should see:
global $customer_id, $order, $sendto, $currency, $cart_PayPal_Standard_ID, $shipping;

if you only see: global $customer_id, $order, $sendto, $currency, $cart_PayPal_Standard_ID;

then replace $cart_PayPal_Standard_ID; with $cart_PayPal_Standard_ID, $shipping;

find:
'shipping' => $this->format_raw($order->info['shipping_cost']),

change to:
'shipping' => $this->format_raw($shiptotal),

find:
'amount' => $this->format_raw($order->info['total'] - $order->info['shipping_cost'] - $order->info['tax']),

replace it with:
'amount' => $this->format_raw($order->info['total'] - $shiptotal - $order->info['tax']),

More...