Are they looking to charge me a % of what I owe the feds?
"A convenience fee of 2.49% of total amount you owe will be charged by our credit card service provider. "
I am at the end and I am tired. is this truly an additional charge?
Yes, using credit card to pay government will always get extra charge. To avoid, you'll have to do direct draw from your bank account, or mailing a check to them.