pewc_check_tax_for_option_price.php

<?php
/**
 * Ensure tax isn't added to options with 'value only'
 */
function prefix_check_tax_for_option_price( $check, $option_price, $item ) {
	if( ! empty( $item['option_price_visibility'] && $item['option_price_visibility'] == 'value' ) ) {
		return false;
	}
	return $check;
}
add_filter( 'pewc_check_tax_for_option_price', 'prefix_check_tax_for_option_price', 10, 3 );