All of the following are functions of the department of Treasury EXCEPT:

The department of Treasury plays a crucial role in managing the financial responsibilities of the federal government. Among its myriad functions, it is responsible for managing federal finances, overseeing currency and coinage, and enforcing federal finance and tax laws. The management of national debt, while related to the Treasury's responsibilities, is not a decision-making function but rather involves maintaining and issuing government securities to finance government operations and manage existing debt levels.

The primary function in determining national debt is handled by other government entities, such as the Office of Management and Budget and the Congressional Budget Office, which assess fiscal policy and budget impacts. Consequently, this distinction clarifies why determining national debt does not align directly with the defined functions of the Treasury Department itself, thus making the identification of this option as the exception valid in this context.