Need Zero Rate Tax based on wholesale user role

I have placed the following code in the functions.php… and I can see that the tax rate is calculated as it should for the four states that we need to apply sales tax to; BUT I cannot charge a wholesale customer sales tax – and so I created a zero rate entry and used this code to capture the ‘wholesaler’ role as well as ‘administrator for testing. I’m still getting charged sales tax. Help please.

/**
 * Apply a different tax rate based on the user role.
 *
 * @param $tax_class
 * @param $product
 *
 * @return string
 */
function woo_diff_rate_for_user( $tax_class, $product ) {

    $current_user = wp_get_current_user();
    $roles = $current_user->roles;
    $current_user_role = $roles[0];

    $not_taxed_roles = array("wholesale", "administrator");

    if (is_user_logged_in() && in_array($current_user_role, $not_taxed_roles)) {

        $tax_class = "Zero Rate";
    }
    return $tax_class;
}
add_filter( "woocommerce_product_get_tax_class", "woo_diff_rate_for_user", 1, 2 );
add_filter( "woocommerce_product_variation_get_tax_class", "woo_diff_rate_for_user", 1, 2 );