The IRS says in this document:
If your functional currency is the U.S. dollar, you must immediately translate into dollars all items of income, expense, etc. (including taxes), that you receive, pay, or accrue in a foreign currency and that will affect computation of your income tax. Use the exchange rate prevailing when you receive, pay, or accrue the item. If there is more than one exchange rate, use the one that most properly reflects your income. You can generally get exchange rates from banks and U.S. Embassies.
If you earned your income throughout the year, you can use the yearly average exchange rates.
You should use the rates published by the US Treasury in this Treasury.gov document.
and stick with the the IRS yearly rate for reported foreign income?
The IRS says in this document:
If your functional currency is the U.S. dollar, you must immediately translate into dollars all items of income, expense, etc. (including taxes), that you receive, pay, or accrue in a foreign currency and that will affect computation of your income tax. Use the exchange rate prevailing when you receive, pay, or accrue the item. If there is more than one exchange rate, use the one that most properly reflects your income. You can generally get exchange rates from banks and U.S. Embassies.
If you earned your income throughout the year, you can use the yearly average exchange rates.