Sales Tax question

I have a client in NY. They need to charge sales tax for orders within NY state. There are literally hundreds of different tax rates throughout the state. Is there some way of integrating a sales tax calculator to the cart for this? I have added several sales tax zones, but to be honest, the zones do not go by any particular input within the cart system. For example, NY City has one sales tax rate. There are hundreds of zip codes in NY City. Just outside of NY City, in Nassau County, there is a different tax rate, but some towns in Nassau County actually share some zip codes as the "other side of town" which is in NY City. In some places, it depends on which side of the street you are on as to which town you are actually in, and the tax rates are different for those two towns.

How does the cart know what to charge to which customer if they don't use "Nassau County", for example (which is one of the sales tax zones I added), anywhere in their customer profile?
This is driving me insane.

This has been discussed. Try a search for New York tax and see the results.

I live in California, and we have similar tax laws.

If the bulk of your sales are outside of NY, then just absorb the few dollars here and there.

Now in one case, I worked for a business (not an online store) that crossed sales through different counties and had sales of over 1 million per year. Let me tell you the State Board of Equalization came at them like slathering dogs.

Thanks, I was just reading a thread about the problem and it seems like it's a real nightmare. My client is very **** about things and I don't think she'll want to "wing it" with the "just use the lowest rate" idea (which to be honest, is what I would do, but....)
I really don't see many options. Even if I manage to find every tax rate for every zone, there's no way to tell the cart which customer is in which zone, based on how NY does things.