motor oil in 5.1 quart jugs

Motor oil, such as Quaker State, is now being sold in 5.1 quart jugs in some stores. What’s the extra .1 about? It’s not 5 liters, because that would be 5.3 quarts.

After a bit of googling, the hard-to-believe consensus seems to be that Wal-Mart has 5 qt bottles exclusively with a bunch of the manufacturers, so they make 5.1 liter bottles to sell elsewhere.