add_action( 'init', 'redirect_login_register' );

function redirect_login_register() {
  global $pagenow;

  if ( $pagenow == 'wp-login.php' && $_GET['action'] == 'register' ) {
    $previous = $_SERVER['HTTP_REFERER'];
    wp_redirect( $previous . 'tudominio.com' );
    exit();
  }
}