Usually just one or two.
For some programs (e.g. University of Adelaide, WSU & CSU), only one interview round is held for all applicants, regardless of their location.
For other programs, a second or possibly even third interview round is also held for applicants who become eligible after first-round interview offers were sent out (e.g. UWA) or for interstate applicants (e.g. Monash).
To check the full list of interview round dates for each program, please refer to the key dates.