We exclude POS transactions from Portion of Sales automatically. In order to reverse this for your store and allow donations from the Portion of Sales campaign to apply to your POS transactions, email us at email@example.com and let us know. We'll set it up for you.
Please note that when you run POS orders, automatically the donation is split among all your selected charities. The only way to select specific charities from your list is through the widget, so it can't be done on POS.