Thanks for the feedback about the POS look and feel.
On the issue you raised about taxes. The POS uses and supports multiple tax tables populated in the Tax functionality for WooCommerce, under the following location:
WooCommerce > Settings > Tax > [Tax Tables]
If you have no tax tables created by the plugin of SimpleSalesTax by Tax Cloud, this is why no taxes are being calculated in the POS.
We don’t have direct experience with the product SimpleSalesTax by Tax Cloud, but a quick review of the WordPress plugin, it appears the plugin is not using the WooCommerce tax table. The plugin is calling their APIs dynamically for the shop front end to provide a tax rate calculation.
The only way the POS could calculate taxes when using the product SimpleSalesTax by Tax Cloud is to build a custom integration with their API services as well, similar to the front end shop. Unfortunately, at this time, we are unable to build this compatibility support for taxes with SimpleSalesTax by TaxCloud. We will add them to a list of requested compatibility products with the POS, hopefully in the future we can provide that compatibility for you.