Commerce Order Total Tax line via EntityMetadataWrapper
the most thorough insight on getting access to the tax line and individual subtotals. found via: https://gist.github.com/BBGuy/3e1f624eaee2088d8eee

// order total object
$order_total_obj = $order_wrapper-&gt;commerce_order_total-&gt;value();
// Order total (cents).
$order_total = $order_total_obj['amount'];
// order currency code
$currency_code = $order_wrapper-&gt;commerce_order_total-&gt;currency_code-&gt;value();
// subtotal without vat
$total_ex_vat = commerce_price_component_total($order_total , 'base_price');
// total tax (in this case vat 20%)
$total_vat = commerce_price_component_total($order_total , 'tax|vat_20');
// subtotal with vat
$sub_total = $total_ex_vat['amount'] + $total_vat['amount'];
// formatted price string with currency sign
$sub_total = commerce_currency_format($sub_total, $currency_code);