If you subscribe to Publisher's Weekly they publish an annual Bestseller issue in which they give sales figures for the top books in each of the big categories. So data on those 500 or so titles is available year by year.
To get a complete picture of sales, though, you'd have to total up the figures for each year the book was sold.
The problem with those figures is that books are returnable, and publishers only know what's been sold to retailers. A big book could have tens of thousands of copies in the distribution pipeline, all of which could in principle be returned at any time.
So when a publisher says, on March 1, 2007, that the 2006 sales for Your Best Book were 252,400 copies, they mean they shipped that net figure, counting all the 2006 shipments less the returns processed through Feb 28. But they could still get 25,000 copies back if the book doesn't continue to sell, because those books are sitting in warehouses and stores, unsold.
Neilsen Bookscan is a better way to know what sales figures are, because they tabulate bar code scan data for actual sales at all the big chains and some independents. Bookscan figures are sales to the public, so returns don't figure into their numbers, but since they don't tract all sales, they too are a guess.
And then you have sales in other countries, plus audio download, book on tape, book club editions, and other special printings.
All in all, it's hard to get sales figures for all but the biggest books.