A player in San Andreas during the Encounter phase must choose whether to visit the Job Board or the Store; they cannot visit both in the same round.

This is supported by the following:

• On page 15:
  "If a player is in San Andreas during the Encounter phase, they may decide whether they would like to visit the Job Board or the Store."

• On page 20:
  "If you have moved into San Andreas, you can Visit the Job Board or go Shopping at the Store (see Encounter Phase pg 10). Remember that you can only perform one action per round!"

These references indicate that during the Encounter phase in San Andreas, a player must choose one of the two options.

Source: pages 15, 20

Source: Core Rulebook (pp. 13, 15, 20, 32, 6)