I recently wrote up a theory about large, rounded numbers in the Torah here.
Then I found an essay by Dr. Eli Mertzbach dealing with these questions in a statistical manner. He additionally wonders at Bamidbar 26:7, אלה משפחת הראובני ויהיו פקדיהם שלשה וארבעים אלף ושבע מאות ושלשים, which I overlooked.
Since my answer cannot account for this, his answer is better than mine (although his answer is not as intuitive, and I cannot comment on the statistical analysis).