I think if you check the Amazon.com online interview questionaire closely, you will find providing your national tax ID is optional.
If your government has a tax agreement with the USA, you may be able to avoid the tax-withholding the US Internal Revenue Service requires Amazon.com to collect on book sales. Providing a foreign tax number is not required (see your tax agreement), it's just the IRS being nosey.
I've just completed the Amazon questionaire myself, and the important thing is to state that you are not a US resident under any of the definitions used by the IRS, and that you are a resident of a country that has a tax agreement with the USA.
How you declare book royalities as part of your personal income on your national tax form depends on the tax law of your country, not the IRS.
Of course, that's just my opinion.
Tony