Is there a way to add manual tax lines at Sales Order Level?

Hi,

Is there any way to add a manual tax line at Sale Order Level. Since the Option 'Allow Tax Applicability' is unchecked at COTO Level to avoid auto tax calculation on transactions. Though I see a 'Tax Classification Code' field at line level but the taxes are not calculating still. We are looking for an option in AR Invoice Level, where the tax lines can be added manually.

Regards

Uday