afaik* (and assuming you are in the US) the official IRS rule is that any transaction involving bitcoin, except transfers between your own accounts as a reportanble transaction.

So if someone paid you via lighting you would need to know the USD market price at the moment of every transaction, as they would be reported as income at that value.

Also, when you spent or converted the btc you would need to know the USD value at that moment and report as either a captol gain/loss (usually as a first in/first out calculation). You can someone game the system on capitol gains tax by selling, then rebuying to capture the loss to get a tax deduction, or accept the gain at a time when you'll pay less in tax for it.

That is all assuming you want to be full legit and have your paperwork ready in case of an audit.

*I am not an accountant, this is info I found while a while back, but I think is still accurate.