Is it worth calculating the U.S. Government dividends (for Oregon taxes) from an IRA withdrawal (Vanguard mutual funds)?

Oregon doesn't tax the interest received from U.S. Government bonds.

I made my first withdrawal from an IRA (at Vanguard) last year and Turbotax is asking me how much of my dividends came from U.S. Government obligations.

Vanguard releases a document each year showing the percentage of the dividends for each mutual fund that came from U.S. government obligations.  Theoretically, I can go back to ALL years I've had the IRA and determine how much of each fund is deductible.  However, my gut says it may not be worth it.

Does anyone have experience with this?  I'm a guy who loves details, but this seems like too much...