Emergency Nursing...Do I have to be certified?

No. You are qualified to sit in for a test to get certifications usually after a year or two working in critical care.

Our ED requires TNCC within a year of hire.

Different ERs require different things. The level one where I used to work required a lot:

BLS
ACLS
ENPC or PALS or APLS
TNCC or BTLS or TNS (trauma nurse specialist - IL-only certification)

CEN (certified emergency nurse) was optional but garnered you an extra $1.00/hour

I now work in a community hospital ER and they require:

BLS
ACLS

and that's it.