How to update Store order totals via AJAX

checkout.html

{exp:store:checkout form_id="checkout_main" next="checkout/confirm"}

	<table class="table">
		<thead>
			<tr>
				<th style="width:60%">Product</th>
				<th>Price</th>
				<th>Qty</th>
				<th style="text-align:right">Total</th>
			</tr>
		</thead>
		<tbody>
			{items}
				<tr>
					<td>{title}</td>
					{if entry_id == 215}
						<td>${item_qty}.00</td>
						<td>1</td>
					{if:else}
						<td>{price}</td>
						<td><input name="items[{key}][item_qty]" value="{item_qty}" class="input-mini" /></td>
					{/if}
					<td style="text-align:right">{item_subtotal}</td>
				</tr>
			{/items}
		</tbody>
		<tbody id="checkout_totals">
			{checkout_totals_snippet}
		</tbody>
	</table>

	<p>{field:billing_country}</p>
	
	<p><input type="submit" name="update_totals" value="Update Totals" /></p>
	
{/exp:store:checkout}

<script type="text/javascript">
$("#billing_country").change(function() {
	// submit the form data via AJAX
	$.post('/checkout/update', $(this.form).serialize()).done(function(response) {
		// update totals
		var response_html = $(response);
		$('#checkout_totals').replaceWith(response_html.find('#checkout_totals'));
		// update XID so it will work more than once
		$('#checkout_main').find('input[name="XID"]').val(response_html.find('input[name="XID"]').val());
	});
});
</script>

checkout_totals_snippet.html

		<tr>
			<th colspan="3">Subtotal</th>
			<th style="text-align:right">{order_subtotal}</th>
		</tr>
		<tr>
			<td colspan="3" class="{if error:promo_code}error{/if}" style="vertical-align: middle">
				Promo Code &nbsp;&nbsp;&nbsp;&nbsp;
				<input type="text" name="promo_code" value="{promo_code}" class="input-medium" />
				{error:promo_code}
			</td>
			<td style="text-align:right; vertical-align: middle;">{order_discount}</td>
		</tr>
		{if tax_name}
			<tr>
				<td colspan="3">{tax_name} ({tax_percent}%)</td>
				<td style="text-align:right">{order_tax}</td>
			</tr>
		{/if}
		<tr>
			<th colspan="3">Total</th>
			<th style="text-align:right">{order_total}</th>
		</tr>

update.html

{exp:store:checkout}
<table>
	<tbody id="checkout_totals">
		{checkout_totals_snippet}
	</tbody>
</table>
{/exp:store:checkout}