What open data sources are available to determine the appropriate sales tax at the state and local levels?
For example, assume that an three items are sold from a retailer to the following destinations:
Is there an open API that provides up to date sales tax information for all of these states and localities?
There are only pay-per-request API's for sales tax data. The Sales Tax Clearing House offers an interface to pull sales tax information. With a list of zip codes, you could automate the process of pulling in the tax data. I'm guessing they probably wouldn't like that, so it would probably be a good idea just to send them an e-mail requesting a data dump.
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I don't know of an API ... but it's really, really difficult ... as a given item might be considered to be a different class for taxing depending on the location. For instance, DC had a few years where prepared ready to eat were subjected to the 'snack tax' (10%) and no longer exempt as food. Some states have 'sales tax holidays' where for a short period specific items are exempted from sales taxes.
The Streamlines Sales Tax Board offers downloads of data from their participants:
http://streamlinedsalestax.org/ratesandboundry/
I've never used the data, so I don't know if it includes municipal and county sales taxes (or if they're removed as part of the 'simplification' agreements)
You might also be interested in exploring a sales tax calculator that the IRS provides for people who itemize their sales taxes. This is based on a black-box formula that estimates total sales tax burden on every day items based on income and household size, and excludes big-ticket items (like a new car) for which the user would presumably know the sales tax. But the reason I recommend it is because it includes the sales tax rates by zip code, so you can make reasonable comparisons by geography.
The calculator itself is here: http://www.irs.gov/Individuals/Sales-Tax-Deduction-Calculator
If you want to look under the hood, the regression coefficients that go into the formula are here: http://users.nber.org/~taxsim/sales-tax-irs-publication-600/
I believe this is the top data provider on the subject of sales tax (part of Thomson Reuters now, used to be a separate company called Sabrix) - http://onesource.thomsonreuters.com/solutions/indirect-tax/ . They definitely have the data, not sure if they expose it as an API though.
