Once again, I find this song sort of interesting in an analytical sense because it only uses three chords, yet I enjoy listening to it.
The verse is entirely in I. However, even though the bass and guitar maintain a repeated riff in that chord, there are strings in the background that add a sense of tension and relief without the main harmonic instruments ever using a cadence. The strings fluidly alternate between chord tones and half steps above them - especially le.
To me, it feels like the song is breathing - inhaling when the strings are creating tension and exhaling when they resolve. This is slightly different from the sensation an actual cadence produces. Some cadences, especially those used by Bach in his organ works, create tension in my whole body, whereas I feel calm during the Nirvana song.
When the song finally switches chords at the chorus, it goes to IV (predictably) and then to five. However, it remains on IV for a long time, which makes the listener feel like IV is in fact tonic. At times, the V chord is held for an especially long time which makees the return to I extra gratifying.