The Keychain relic action doesn't appear to calculate its value correctly, The value it shows as being "10 minutes of taxes at maximum food production" is less than a quarter of a second of my current tax income, which is far from max food production. With the other component being even smaller, this is such a comically ineffective ability that it seems like it must be a bug.
By napkin math, it looks like it might be getting 10 minutes of raw coin income but not including gain multipliers like Investment, Golden Throne, treasure, etc.