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If you're querying the IRS for tax rates every time you run a calculation, you're doing it wrong.

If you aren’t querying exchange rates often - you’re also doing it wrong....

Depends on what you're using the exchange rates for. The rates used by Visa only change once per day, as an example.

And you still wouldn’t store that locally. You may cache it locally - something you could also practically do with lambda.

Well yes, the parent we're replying to was talking about caching.