sandbox.php

<?php
    require_once 'app/Mage.php';
    umask(0);
    Mage::app();

    //Test Variables
    $item['sku'] = 'Avent-Soothie-AD-SCF190/01';
    $item['qty'] = 2;
	$orderIncrementId = '100003301';
    
    $storeId = 1;
    $store = Mage::app()->getStore($storeId);


    $order = Mage::getModel('sales/order')->loadByIncrementId($orderIncrementId);
    $quote = Mage::getModel('sales/quote')->load($order->getQuoteId());

    $product = Mage::getModel('catalog/product')->loadByAttribute('sku',$item['sku']);
    			
    $quoteItem = Mage::getModel('sales/quote_item')->setProduct($product)
				->setQuote(Mage::getModel('sales/quote')->load($order->getQuoteId()));
	
	$orderItem = Mage::getModel('sales/convert_quote')->itemToOrderItem($quoteItem)->setProduct($product);

	$productPrice = $product->getPrice();
	$qty = $item['qty'];


	//Tax in formation
    $taxClassId = $quote->getCustomerTaxClassId();
	$taxCalculationModel = Mage::getSingleton('tax/calculation');
    $request = $taxCalculationModel->getRateRequest($quote->getShippingAddress(), $quote->getBillingAddress(), $taxClassId, $store);

	$rate = $taxCalculationModel->getRate($request->setProductClassId($product->getTaxClassId()));


    $rowTotal = $productPrice * $qty;
	$tax = ($rowTotal * $rate)/100;

	$orderItem->setPrice($productPrice);
	$orderItem->setBasePrice($productPrice);
	$orderItem->setBaseOriginalPrice($productPrice);
	$orderItem->setOriginalPrice($productPrice);
	$orderItem->setQtyOrdered($qty);
	$orderItem->setTaxPercent($rate);
	$orderItem->setTaxAmount($tax);
	$orderItem->setRowTotal($rowTotal);
	$orderItem->setBaseRowTotal($rowTotal);	
	$orderItem->setOrderId($order->getId());
	$orderItem->setOrder($order);
	$orderItem->save();
	$order->addItem($orderItem);
	$order->save();

	$oItems = $order->getAllItems();
	$subTotal;
	$grandTotal;
	$taxTotal;

	foreach ($oItems as $oItem)
	{
		$subTotal  	+= $oItem['row_total'];
		$taxTotal  	+= $oItem['tax_amount'];
		//print_r($oItem);
	}
		$grandTotal += $subTotal + $taxTotal + $order->getShippingAmount();

	//$comment .= "Added item(SKU): " . $sku . "<br />";


		$order->setSubtotal($subTotal)
		  ->setBaseSubtotal($subTotal)
		  ->setGrandTotal($grandTotal)
		  ->setTaxAmount($taxTotal)
		  ->setBaseGrandTotal($grandTotal);

		$order->save();

?>
<pre><?php print_r($order) ?></pre>

<pre><?php echo($subTotal) ?></pre>
<pre><?php echo($taxTotal) ?></pre>
<pre><?php echo($grandTotal) ?></pre>