Techknitting shows us how to do a tubular cast off when knitting in the round.
Techknitter writes:

Knitters often complain that their casts on look so different from their casts off, but after this post, YOU, dear reader, will no longer be able to complain about this particular annoyance. In examining the exposed fabric edge, the most eagle-eyed expert will find it impossible to say whether your tubular ribbing edges were created by a cast ON or a cast OFF.

To find out how to tubular cast on, visit the Techknitting blog here – Link.