This information is available from your financial institution, be it a brokerage like Wells Fargo or direct from the mutual fund company, like American Funds.
You should be able to find a Tax Center or something similar on the company's web site.
It may be called Tax Center, Tax Worksheets, Tax Calculators, or something similar.
I know that on the American Funds site, it is called Tax Center, and there is a link specifically for "Sales Tax Exclusion for U.S. Government Income."
The worksheet / calculator should list the specific funds that are tax exempt.
Funds may be partially or 100% exempt.
Hope this helps.
