The new automated sales tax feature is very accurate so long as you remember a couple things.
1. It's best to use the FULL zip+4 zip code whenever possible. This will help QBO get exact location for local city, county, etc. taxes.
2. When you setup the sales tax in QBO, click the drop down menu and scroll down to CO. You'll see there are lots of cities there. Select the city, NOT the state of CO. This will also help to make sure that it calculates local taxes correctly. (picture below)