MINEOLA — Nassau Executive Edward Mangano and the Civil Service Employees Association Local 830 announced Friday an agreement that will allow more than 5,000 county employees as many as 60 unpaid volunteer furlough days in an attempt to close Nassau’s budget gap. Officials said the program will be offered to full-time union employees who can take up to 20 consecutive days off at a time. Mangano said the deal will provide an opportunity for both the county and taxpayers to save money.