For TaxJar to work well with ShopSite, we need addresses with 9-digit zip codes.
Here's what a tech person at TaxJar wrote:
The ShopSite integration does use the SmartCalcs API so I can confirm that you are also using the SmartCalcs API. However, since the ShopSite integration is managed by a 3rd party, we are unable to guarantee their implementation and therefore cannot promise the Accuracy Guarantee would cover you in this scenario.
I took a look at the logs associated with your account and see that ShopSite is passing us the Country, City, and Zip Code but not the street address. In many scenarios, if you are unable to get a 9 digit zip code, having the full street address included in sales tax calculations will get you a higher level of accuracy.
You may want to reach out to ShopSite support to request they update their integration to include the full street address in the sales tax calculations for greater accuracy.
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For states like California which have a complicated collection of tax collection localities, we must correctly collect sales tax.
Since many people don't even know their 9-digit zip code, we need a ShopSite add-on that will check the customer's address, preferably while they're entering it, supplying their full zip code. Such add-ons already exist for other shopping carts.