Tax configuration in the United States

This advice should work for state with a single rate of sales tax.

FIRST, set your store’s zone properly:
Admin > Configuration > My Store > Zone
Choose your country and zone from the lists provided by the edit button.

Here is an example, for setting up taxes for the state of Colorado:

Go to:

Admin > Locations/Taxes > Zones Definitions > Insert

Zone Name: Colorado
Description: Colorado State Sales Tax (or whatever you like)
click on ‘insert’

Click on ‘Details’ after creating a zone
Click on ‘Insert’
Country = United States
Zone = Colorado
Click on ‘insert’

Go to:
Admin > Locations/Taxes > Tax Classes

Click on ‘New Tax Class’
Title = Taxable Goods
Description = Whatever you like
Click on ‘insert’

Go to:
Admin > Locations/Taxes > Tax Rates

Click on ‘New Tax Rate’
Select your zone, ‘Colorado’
Set your tax rate
give it a description, ex: Colorado State Sales Tax
Click on insert

Last, make sure you apply the new tax class that you created (Taxable Goods) to any and all products that you might be charging tax on.

To make this faster when adding new products, in the Admin area, you can select a default Tax Class to be applied to all new products you create.
Go to Admin > Catalog > Product Types, then choose a product type (likely Product - General), and click Edit Layout, then Default Tax Class.