Taxing district boundaries don't follow zip+4 they follow whatever boundaries they were created with.   Hell state lines don't follow zip +4.   

But even if you had 100% perfect knowledge of every rate, boundary, and exemption said business would be required to mail and fill out sales tax forms for thousands of taxing entities.   Just within Colorado the business could be remitting sales tax (and be audited by) 3000+ sales tax collecting entities.

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