function gettax($order_id){

        $order_query = $this->db->query("SELECT * FROM `oc_order_total` WHERE `order_id` = '" . (int)$order_id . "' AND code ='shipping'");
        return $order_query->row;
    }

    function getOrderProduct($order_id){

        $order_product = $this->db->query("SELECT * FROM `oc_order_product` WHERE `order_id` = '" . (int)$order_id . "'");
        return $order_product->row;
    }

$this->load->model('checkout/order');
            $data['orderDetails'] = $this->model_checkout_order->getOrder($this->session->data['order_id']);

            $data['ordertax'] = $this->model_checkout_order->gettax($this->session->data['order_id']);

            $data['orderProduct'] = $this->model_checkout_order->getOrderProduct($this->session->data['order_id']);

<script type="text/javascript">
ga('require', 'ecommerce');
ga('ecommerce:addTransaction', {
  'id': "<?php $orderDetails['order_id'];?>",                     // Transaction ID. Required. dynamic variable of order id
  'affiliation': "<?php $orderDetails['store_name'];?>",   // Affiliation or store name. Kuberan Silks
  'revenue': "<?php $orderDetails['total'];?>",               // Grand Total. grand total dynamic variable of the price
  'shipping':"<?php $ordertax['value'];?>" ,                  // Shipping. dynamic variable of shipping
  'tax': "<?php $orderProduct['tax'];?>"                     // Tax. dynamic tax variable
});

ga('ecommerce:addItem', {
  'id': "<?php $orderProduct['order_id'];?>",                     // Transaction ID. Required.
  'name': "<?php $orderProduct['name'];?>",    // Product name. Required.
  'sku': "<?php $orderProduct['model'];?>",                 // SKU/code.
  //'category': 'Party Toys',         // Category or variation.
  'price': "<?php $orderProduct['price'];?>",                 // Unit price.
  'quantity':"<?php $orderProduct['quantity'];?>"                  // Quantity.
});

ga('ecommerce:send');
</script>