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OK, here is an idea.

Make a numeric field on that Employee Table called Round Robin #.  Make it Unique.  Assign Each employee eligible for assignment with a number starting at 1, in sequence.

You will need a Helper Table called # Active Employees with a single record in it ([Record ID#] = 1)  and then make a relationship down to the "Ticket's" record with a formula field on the Ticket's table  with a formula of 1 to connect it to the Tickets.  Also Make a similar relationship to Employees. 

Make a summary field on  # Active Employees table to count the number of Active employees. Look that up down to Tickets.

(note you can avoid the helper table buy using a Formula Query formula to count up the number of Active Employees).

OK, so have all the ingredients now.

On your form, make a calculated field for the Assigned Employee Sequence #.

The formula will be REM([Record ID#], [Total number of active employees] +1)

Now will see that there is a riound robin number assigned to each Ticket.

Lastly you will need a Pipeline to trigger when a Ticket is created and the assigned employee is blank.  It will search the Employyes table looking for the calculated Sequence number on the Ticket (limit to 1 record in the search), and then assign that employee to the ticket.

Another way to go on this would be a dedicated table for a round robin candidates where the key field of the table is that sequence number. If you did that, then you could directly look up the Round Robin employee from that table down into your tickets with a form rule. 

Feel free to post back if you want some more help from this. These are just some ideas that come to mind but there's definitely a way to do this.