Do MMA judges score all rounds at the end of the contest, or do they score each round at the end of each round?

If the competition follows the Unified Rules of MMA, they are based on the ABC Ring Officials Certification Program, and this states:

1. COMPLETION OF THE SCORECARD
   If the referee indicates that a contestant has been knocked down, it must be scored as a knockdown. The referee is the only official that can penalize a contestant for a foul. Judges must deduct points for infractions when the referee officially designates a foul and point deduction.
   Double-check your math before handing your scorecard to the referee. If a mistake was made by you on the scorecard, correct and initial your scorecard and inform the referee of your mistake and correction.
   Fill out the scorecard in its entirety, enter the points, and turn it over to the referee.
   The referee will pick up the cards after each round and turn them over to the Athletic Commission Supervisor.

It should be noted, however, that within the Unified Rules of MMA themselves, how a round is to be scored is specified, but what happens to the scorecard per round or bout is not.

A Bloody Elbow article (one of the leading MMA sites) from 2007 states:

Following the end of every round the judges turn their cards in to the ref who holds them to make sure that no score changing happens "after the fact." Of course...with boxing's history there are plenty of fights that can be pointed to as examples of where people feel that score changing DID happen. But that is neither here nor there I suppose.

At the end of the fight each judge's card is totaled with the fighter with the most points on that card being the winner. You need to win at least 2 of the 3 judges scorecards to get a win. So, winning on one card and the other two cards being a draw would mean it was a "majority draw."

So the judges must enter a score at the end of each round, and those scores are checked by the referee to make sure they're not tampered with afterwards.

The score for each individual round must be written down at the end of the round. A judge cannot go back and change the score after the fact.