Configuring Sales Tax is a bit complicated both from the perspective of trying to understand the various state regulations (I'm referring to United States) and from the perspective of configuring ZenCart to apply those rules.

Since the regulations varies from state to state, you should consult with your tax advisor as to how much tax and from which customers you want to collect sales tax from.

General sales taxes can be found on Wikipedia. But you usually will want to look directly to the official state government website. California's is called the Board of Equalization. Florida provides a nice matrix of the various situations for merchants. You can find links to these government reference sites and general information from SalesAndUseTax.com.

Many state will have a base tax rate and then each county within that state has an added tax surcharge. For example Florida. These are known as local tax. Local tax for Durango, Colorado for example is found on their City website.

If you are merchant and need to collect local tax (say from customers that are local to your store), you can install the ZenCart local tax module. By "ZenCart Admin -> Locations / Taxes -> Local Sales Tax", you can configure this mod to look check the zipcode or the city to determine if the customer is "local" or not (and hence charged a local tax or not). To determine what city are in what county, and what zip codes are in what cities, either BrainyZip.com or MelissaData might help. This surcharge tax configured in the mod is applied on top over any base state tax you have configured.

For customers that are non-local but within your state, you can configure Zencart to charge state base tax by ZenCart tutorial here.

You may need to determine which product is taxable or not. Here is an example. But this varies from state to state. This will determine which "tax class" your product is in. If all your products are taxable, then you only need one tax class under "ZenCart admin -> Location / Taxes -> Tax Classes". And that would be "Taxable Goods".

After setting up the tax class, set up your Zone by "Locations / Taxes -> Zone Definition". And next set up your Tax Rate, which requires specifying both the Tax Class and the Zone.