Jesus did say, "Render unto Caesar that which is Caesar's and unto God that which is God's."
Any thinking person would ask, "Who is Caesar in America? We don't have an Emperor..."
A thinking Christian would look to further revelation, most will go to Romans chapter 13 and plant their stake there.
[Rom 13:5-7] 5 Wherefore [ye] must needs be subject, not only for wrath, but also for conscience sake. 6 For for this cause PAY YE TRIBUTE also: for they are God's ministers, attending continually upon this very thing. 7 RENDER THEREFORE TO ALL THEIR DUES: tribute to whom tribute; custom to whom custom; fear to whom fear; honour to whom honour.
When the Christian plants their stake in Romans 13 and refuses to move because they have been programmed by the State and won't even ask, "Who is Caesar in America?" they will call me, a Christian Bible teacher "seditious" if I say, "Taxation is legalized theft, Caesar is not the government, and the people who are robbing the taxpayer set the system up so they themselves don't have to be robbed."
In the USA Caesar is not a person, a system, or a group; in America Caesar is a document, the Constitution. Anybody who believes that the 16 "Amendment" makes the federal income tax lawful doesn't know the history behind the 16 "Amendment."
Look up "The Law That Never Was" by William J. Benson and Martin J. "Red" Beckman. They have some lectures posted on YouTube.
All that being said, when Jesus said, "Render unto Caesar..." he was telling them to pay their taxes to Caesar's government.