Set your Country of Operation to United States
When the owner creates the TuitionDesk organisation, they set the Country of Operation to United States. That one setting switches billing currency to USD, sets Stripe as the payment processor with Cards and ACH as local payment methods, and lets the owner pick their own US timezone and the MM/DD/YYYY date format — configured once per organisation. There's no single national tax rate: TuitionDesk doesn't set a default for the US because sales tax varies by state, so the owner sets whatever rate applies to them.