WooCommerce Check Cart Quantity

gistfile1.txt

// check that cart items quantities totals are in multiples of 5
add_action( 'woocommerce_check_cart_items', 'woocommerce_check_cart_quantities' );
function woocommerce_check_cart_quantities() {
  global $woocommerce;
  $multiples = 5;
    $total_products = 0;
    foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) {
        $total_products += $values['quantity'];
    }
    if ( ( $total_products % $multiples ) > 0 )
        $woocommerce->add_error( sprintf( __('You need to buy in quantities of %s products', 'woocommerce'), $multiples ) );
}