You can change the Tax Class Settings or Base Currency for a Multi-Site, Client Site, or Site. Site settings override what you have set as defaults.
Follow the path below to configure these settings.
Sites (Client) > Select site > Billing > Billing Settings & Preferences > Billing Settings Section
Here you can change the Default Tax Class and the Currency and Payment Terms.
Please see this article for more information about site-specific billing settings on this screen.