Yes you need to config the Show tax in cart in order to get tax to show and I think you also need to config the display of prices to show tax
<?php if (VmConfig::get ('show_tax')) { ?>
<?php if (VmConfig::get ('show_tax')) { ?>
<td align="right"><?php echo "<span class='priceColor2'>" . $this->currencyDisplay->createPriceDiv ('taxAmount', '', $this->cart->pricesUnformatted[$pkey], FALSE, FALSE, $prow->quantity) . "</span>" ?></td>
<?php } ?>
<td align="right"><?php echo "<span class='priceColor2'>" . $this->currencyDisplay->createPriceDiv ('discountedPriceWithoutTax', '', $this->cart->pricesUnformatted[$pkey], FALSE, FALSE, $prow->quantity) . "</span>" ?></td>
<td colspan="1" align="right">
<?php
// Quorvia no need for this rubbish!
//if (VmConfig::get ('checkout_show_origprice', 1) && !empty($this->cart->pricesUnformatted[$pkey]['basePriceWithTax']) && $this->cart->pricesUnformatted[$pkey]['basePriceWithTax'] != $this->cart->pricesUnformatted[$pkey]['salesPrice']) {
// echo '<span class="line-through">' . $this->currencyDisplay->createPriceDiv ('basePriceWithTax', '', $this->cart->pricesUnformatted[$pkey], TRUE, FALSE, $prow->quantity) . '</span><br />';
//}
//elseif (VmConfig::get ('checkout_show_origprice', 1) && empty($this->cart->pricesUnformatted[$pkey]['basePriceWithTax']) && $this->cart->pricesUnformatted[$pkey]['basePriceVariant'] != $this->cart->pricesUnformatted[$pkey]['salesPrice']) {
// echo '<span class="line-through">' . $this->currencyDisplay->createPriceDiv ('basePriceVariant', '', $this->cart->pricesUnformatted[$pkey], TRUE, FALSE, $prow->quantity) . '</span><br />';
//}
echo $this->currencyDisplay->createPriceDiv ('salesPrice', '', $this->cart->pricesUnformatted[$pkey], FALSE, FALSE, $prow->quantity) ?></td>
You are not placing the override in the right place if it only functions if you hack the default views
They should be placed in:-
\templates\your template\html\com_virtuemart\cart\