These two pages may be of some help :
Selling ibooks : http://www.apple.com/itunes/working-itunes/sell-content/books/
Authors FAQ : http://www.apple.com/itunes/working-itunes/sell-content/books/book-faq.html
The second link includes :
A valid U.S. Tax ID is required if you would like to sell books on the iBooks Store and you are an individual who primarily lives or works in the United States, or you are a company or organization. If you only want to offer books for free, or you are an individual who is not based in the United States, you don’t need a U.S. Tax ID. Learn more about U.S. Tax IDs (EINs).
We will send you an email after we complete verification of your U.S. Tax ID and legal entity name. If we find that the U.S. Tax ID and legal entity name does not match the records of the U.S. Internal Revenue Service, you will be required to update your tax information in Agreements, Tax, and Banking on iTunes Connect.
So if you aren't in the US then you shouldn't need a US Tax ID