In standard funktionality, if using Income/Expenses on POS, there is no possibility to setup that this should be posted with sales tax.

In business, most of the companies don´t want to post this expenses on bridging accounts and then post finally with sales tax in Accounting and journals.

Most of the scenarios is, that as soon as the Expenses (e.g. Post) are posted via POS , it should already have sales tax on this entry. So it would need the setup for sales tax groups on the Expenses directly.