Do you need a sound card?
Answer is depends on what you need in a sound card and what you intend to do with the sound card? Are you doing recording purposes? Are you trying to do sound editing? Or are you just using it for gaming and music purposes?
If you are using just for gaming and music/movies, best is to have a good pair of speakers to pair up with a sound card.
Rubbish speakers usually will give you crap sound even if you use a high end sound card. Vise versa.
It must go hand in hand and make a good pairing.
My suggestion is i rather you save up the money and go for a better speakers. A high end 2.1 or 5.1 whichever. Then plug in to your onboard sound. If you like the sound then fine. If you do not like the sound for so whatever reason then just grab a sound card. But believe me, if you aint a audiophile, you cannot hear the difference.