Trevor the Guru here!
When taxes aren't charging at the checkout, this normally falls down to one of two things. The first option could be the location you're testing with. Most merchants only have taxes set up for certain regions so if you're testing a checkout with a location that has 0% setup this could be why you're not seeing taxes charged. The second thing that could be causing this is a tax setting found in Settings/Taxes. This option is titled "All taxes are included in my prices" if this is enabled, then taxes won't charge as the system thinks that your taxes are built into the price so it won't double charge.
If neither of these is the culprit to your issue, then feel free to shoot us an email at firstname.lastname@example.org from the email on the account and we'd be happy to take a look!
All the best,