The figures indicate that sales of Tolkien's books have surpassed 600 million. Counting Tolkien's book sales have been notoriously difficult due to poor accounting, legions of unauthorised overseas editions and even pirate editions of the book being sold in the United States (most famously the Ace Books edition of 1965, which sparked an international outcry and helped catapult Tolkien to greater fame and success in the States), so even this is a conservative figure.
Sales of 600 million would put Tolkien comfortably in the top ten selling authors of fiction of all time, although (contrary to some reports) nowhere near the top. William Shakespeare's plays have sold over 4 billion copies, whilst Agatha Christie's novels have sold at least 2 billion and possibly closer to 4 billion copies. From there it's a steeper drop to Barbara Cartland, who has sold around 750 million copies of her romance novels, just ahead of Danielle Steel on an estimated 700 million. Harold Robbins and Georges Simenon are around 700 million apiece as well.
Tolkien's sales put him at approximate parity with Enid Blyton, Sidney Sheldon and J.K. Rowling, who are all between 500 and 700 million in sales, and comfortably ahead of the likes of Dr. Seuss, Leo Tolstoy, Jackie Collins, Dean Koontz and Stephen King. Tolkien's friend C.S. Lewis can only muster 200 million sales of his books.
However, although Tolkien may not be the biggest-selling novelist of all time, he may have the biggest-selling individual novel. The overwhelming majority of Tolkien's book sales come from The Lord of the Rings, which across all editions and both the three and one-volume versions of the text has sold almost half a billion copies. The Hobbit has sold over 100 million copies. The combined sales of all of Tolkien's other books, although still respectable, fall well short of those figures.
Among contemporary and recent fantasy authors, George R.R. Martin, Sir Terry Pratchett and Robert Jordan have achieved just short of 100 million sales apiece.
ETA: The One Ring has clarified their report as an "April Fool's" gag, a bit of a non-sequitur one since the figures are actually fully credible (if anything, on the conservative) side of things: Tolkien had sold over 400 million books by 2001, so an additional 200 million sales in twenty years, a period when Tolkien's popularity exploded beyond all recognition due to the success of the films (and HarperCollins were attributing a 50 million boost in sales as early as 2003), is pretty easy to believe.