Spoke too soon - using the code in the thread - includes/classes/order.php replaced all lines between
/*********************************************
* Calculate taxes for this product
*********************************************/
and
/*********************************************
* END: Calculate taxes for this product
*********************************************/
with
if (DISPLAY_PRICE_WITH_TAX == 'true') {
$shown_price = (zen_add_tax($this->products[$index]['final_price'], $this->products[$index]['tax']))
+ zen_add_tax($this->products[$index]['onetime_charges'], $this->products[$index]['tax']);
$this->info['subtotal'] += $currencies->value($shown_price)* $this->products[$index]['qty'];
} else {
$shown_price = (zen_add_tax($this->products[$index]['final_price'] * $this->products[$index]['qty'], $this->products[$index]['tax']))
+ zen_add_tax($this->products[$index]['onetime_charges'], $this->products[$index]['tax']);
$this->info['subtotal'] += $shown_price;
}
$this->notify('NOTIFY_ORDER_CART_SUBTOTAL_CALCULATE', array('shown_price'=>$shown_price));

This has solved issue in shopping cart and sub total but issue remains in shopping cart contents section of checkout_confirmation
Where does the code need to be changed to solve this?