Green’s Dictionary of Slang

a goodbye, the act of saying goodbye.

1975		‘P.B. Yuill’ Hazell and the Three-card Trick (1977) 130: Try to bung him a few quid for an accomodation and you could say ta ra to your teeth.
1998		K. Sampson Awaydays 62: Birkenhead park, where the tunnel bus dropped us and where we’d said our ta-ras.