If you register with a new account through the app, you're supposed to provide the SSN of the business owner for tax reporting purposes. The help item says the following:

Why is my income reported to the IRS?
With Amazon Local Register, you earn income through credit card transactions processed by Amazon Payments. Amazon Payments is required by law to report all income to the IRS using form 1099K. A copy of this form will be delivered to the mailing address you provide at the end of the year. If you have questions about this information, please consult your tax advisor.

I don't like the line, "required to report ALL income."

Edit: Vinhboy's post above seems to clarify.