private function _getPreTaxAndShippingOrderAmountFromStdIn() 
    {
        print PHP_EOL . "-------------------------------------------" . PHP_EOL;
        print "Enter the pre tax amount to charge for the order" . 
              "as a number (to 2 decimal places): ";
        do {
            $orderAmount = trim(fgets(STDIN));
        } while (!is_numeric($orderAmount));

        return $orderAmount;
    }