Yes, NATO is still needed in the post-Cold War era, because NATO still serves an important purpose in providing a forum for people to air differences without it escalating into war. The war of ideas still remains. Communism is still a constant threat. Without NATO, this battle of ideas could escalate into war, rather than discussion.
Yes, NATO is still needed in the post-Cold War era, because there are lingering conflicts between these nations, that might flare up again without NATO. There remains tension between Russia and the United States, especially as Russia has re-emerged as a world power. Finding a forum for these and other disputes makes organizations like NATO critical, even in the post-Cold War era.
Let's be honest, no one has ever been "communist" at least the way Marx and Engels intended it to be. The only relics of the cold war I see today are North Korea, which NATO has never addressed. The Warsaw Pact has been dissolved, and Modern day Russia obviously does not equate to the Soviet Union. China, a "communist" country in name only has not been communist in a Maoist sense since the 1980s. It is a well known fact that the PRC moved to capitalism, and never stuck to old Maoist principles. NATO, as it was originally formed is not needed Post-cold war.