Here's the Padevsky-Botvinnik game. A lot of ctr play/pressure here:

[Event "Alekhine mem"]
[Site "Moscow"]
[Date "1956.??.??"]
[Round "?"]
[White "Padevsky, Nikola"]
[Black "Botvinnik, Mikhail"]
[Result "0-1"]
[ECO "B88"]
[PlyCount "50"]
[EventDate "1956.??.??"]
[Source "ChessBase"]

1. e4 c5 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 d6 6. Bc4 e6 7. O-O Be7 8.
Be3 O-O 9. Bb3 Na5 10. f4 b6 11. Qf3 Bb7 12. g4 Rc8 13. g5 Rxc3 14. bxc3 Nxe4
15. Qg4 Qc8 16. Rf3 Nxb3 17. axb3 f5 18. Qh4 e5 19. Rh3 h6 20. Qh5 Qxc3 21. Rd1
exd4 22. Bd2 Qc6 23. gxh6 Ng5 24. Rg3 Qh1+ 25. Kf2 Ne4+ 0-1

Another game, from a najdorf  move order, with e5 being forced. Rxc3 sac helped to play d5 break later in the game:

[Event "URS-ch sf"]
[Site "Sverdlovsk"]
[Date "1957.??.??"]
[Round "5"]
[White "Gipslis, Aivars"]
[Black "Simagin, Vladimir"]
[Result "0-1"]
[ECO "B88"]
[PlyCount "114"]
[EventDate "1957.??.??"]
[Source "ChessBase"]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bc4 e6 7. O-O Be7 8. Bb3
Nc6 9. f4 Nxd4 10. Qxd4 O-O 11. Kh1 b5 12. a3 Bb7 13. f5 e5 14. Qd3 h6 15. Be3
Rc8 16. Rad1 Rxc3 17. bxc3 Bxe4 18. Qe2 Qc8 19. c4 bxc4 20. Bxc4 Bb7 21. Bb3 d5
22. Bc1 Bd6 23. Bb2 Bb8 24. Rd3 d4 25. Rg3 Rd8 26. Bc1 e4 27. Bf4 Bxf4 28. Rxf4
Bd5 29. Bxd5 Rxd5 30. Rxe4 Nxe4 31. Qxe4 Qxf5 32. Qxf5 Rxf5 33. Kg1 Rc5 34. Rd3
Rc4 35. Kf1 f5 36. Rd2 Kf7 37. Ke2 Ke6 38. Kd1 Kd5 39. Re2 Ra4 40. Re7 g5 41.
Rh7 Rxa3 42. Rxh6 d3 43. cxd3 Ra2 44. g3 Kd4 45. Rf6 Kxd3 46. Ke1 Ke4 47. h4 g4
48. Kf1 Kf3 49. Rxf5+ Kxg3 50. h5 Ra1+ 51. Ke2 a5 52. h6 Rh1 53. Rf6 a4 54. Ra6
Rh5 55. Ke3 Kh2 56. Rg6 g3 57. Kf3 Rh3 0-1

Its more of a positional sacrifice rather than a tactical one.

It aims to break & weaken white's Q-side pawn structure so to facilitate an attack on the king or the doubled QKt pawns. With this point in particular in mind, you will see it esp in a lot of dragons cos of black's fianchettoed KB & the semi open c-file. But such a plan can also be applied in a non dragon case where white castles Q-side.

The other point being play for pressure on the ctr. Notice after eliminating the c3 Kt, black also more often than not will capture the e-pawn with his f6 kt immediately. The absence of W's c3 kt also can facilitate the advance d5 if its part of your plans to do so esp after e5 had been played or forced beforehand.  Being a Najdorf player myself, this ctr play is what I aim for when I dream up a Rxc3 sac.  Your minor pieces will need to be developed in such a way so as to actively take charge of the ctr after the sac is made. (same principles apply for the Q-side attack case above)

You can check out Padevsky-Botvinnik Moscow 1956 for a non dragon Rxc3 sac. Neither did white castle Q-side.

One sacrifice that I see happening fairly often in the open sicilian is a rook sacrifice for white's knight on c3.

If I am playing the najdorf/scheveningen system (5. ...a6 and then 6. ...e6 move order), would there be a set of conditions in which I would play such a sacrifice?  Or is this only a standard sac in lines with a fianchetto'd KB?

Also, are there any white anti-sicilian lines in which black would consider such a sacrifice?