First of all, the retirement of the employee, particularly as the misconduct alleged is fraud, has to be subject to such action as per rules depending on the outcome of the disciplinary action. You can withhold gratuity till the decision of the departmental inquiry by passing a specific order to that effect and subject to the provision that in case the employee is exonerated of the charges, he shall be paid gratuity along with interest as notified (10% simple interest).