Might be a bit late on this one, but there doesn't seem to be a posted solution online. You can remove the tax line using the below.
In your template.php file use the below, this should hide it from your order confirmation email as well. I haven't noticed any problems from this modification, but ymmv. The variation from the standard code is: $rows = array_splice($rows, 2);
function THEME_commerce_price_formatted_components($variables) {
// Add the CSS styling to the table.
drupal_add_css(drupal_get_path('module', 'commerce_price') . '/theme/commerce_price.theme.css');
// Build table rows out of the components.
$rows = array();
foreach ($variables['components'] as $name => $component) {
$rows[] = array(
'data' => array(
array(
'data' => $component['title'],
'class' => array('component-title'),
),
array(
'data' => $component['formatted_price'],
'class' => array('component-total'),
),
),
'class' => array(drupal_html_class('component-type-' . $name)),
);
}
$rows = array_splice($rows, 2);
return theme('table', array('rows' => $rows, 'attributes' => array('class' => array('commerce-price-formatted-components'))));
}