So long as you have multi-game series.. the league will always want a series to go the distance. I have no doubt in my mind that the NBA will give a bit of a "nudge" to the team whose win would help get another game in the playoffs.
.. and while that is a form of "rigging", it's not specifically trying to help specific teams. You have to know that if your team is up 3-0, and with another win the NBA would lose THREE games.. thennyes, they're going to give some calls to the team that's down three games. Sometimes that works for you, sometimes, it works against you.
So the NBA isn't really rigged..
..except when it comes to the Houston Rockets and the NBA Draft..