If you made the contribution via payroll then you should receive tax/PRSI relief via payroll. If you made it from after tax income then you will need to claim tax and PRSI relief yourself. Check with your payroll department as to which way they did it.
You don't get to keep any of it, the whole 10,000 goes into your pension
If you had taken it in cash, you would have gotten 5,400, the taxman 4,600.
You get 10,000 into your pension at an effective cost to you of 5,400