WASHINGTON — Final campaign finance tallies trickled out Thursday for a presidential race expected to be the most expensive in U.S. political history, showing a last-minute $10 million contribution to a political action committee backing Republican candidate Mitt Romney from a billionaire Las Vegas casino magnate who has been the election’s biggest moneyman.

The $10 million donation by Sheldon Adelson to the Restore Our Future “super” PAC raised the casino owner’s total contributions for the 2012 campaign to at least $72 million, all for Republicans....