How do I find the amount of sales taxes I collected so that I can report it to the government?

The Sales Report is the one you are looking for. This report provides you the key metrics to understand your taxable and non taxable sales. 

It shows you how much sales tax you've collected. It also describes all of the payments and payment types you have received. 

Also, for you guys that use recurring billing, a section will show you the amount of revenue collected for those subscriptions. One stop shopping for all things sales.