How do I round $9.00?
This question is somewhat unclear as Rachel points out, tho I suspect the answer is "$9" (nearest dollar). "$10" would be rounding to the nearest "tens of dollars".
Strictly speaking, "$9.00" is rounded to the nearest cent (penny). Rounding to the nearest dollar would be "$9".
This is a confusing question because you did not say what to round $9.00 to. It is already rounded to the nearest dollar, so I'm not sure how to answer except that you could round it up to $10. Can you provide the original problem/question so that we can better help you?