Just as a test run, I went all the way to the final "process payment" screen on payusatax.com with a debit card. On the second to the last screen, I got a message that said: "Your card is eligible for processing as an ATM/debit transaction. If you would like to process your payment as a ATM/debit transaction, press the continue button. If you would like to process your payment as a debit card, press the process as debit card button."

I tried both, and there was no apparent difference in how it handled the transaction -- although I didn't do the final step. In neither case was I asked for a PIN.