I don't think it's 5% for each failure to file and failure to pay. If I recall correctly, the failure to file penalty is 5% of the amount owed per month, for the first 5 months, then 0.5% per month after that. The failure to pay penalty is 0.5% per month, except that no failure to pay penalty is assessed in any month where the 5% failure to file penalty is assessed.
So the net penalty is 5% per month for the first 5 months, then 1% per month after that.
Plus, there is interest owed on the amount of tax due AND on the penalties, at a rate of about 0.5% per month, so the net result is something like 28% after 5 months, growing an additional 2% per month after that. (The interest will eventually overwhelm the penalties.)
And then if he won't file 2019 either, that sets up a whole separate penalty and interest calculation. And so on.
