Eratosthenes of Cyrene (220 BC), is the first guy who actually measured the earth diameter. So he already knew that the earth is round. In fact, Pythagoras (around 523 BC) had proposed that the earth is round, although nobody knows how he got his ideas from.
It is save to say that at the time the bible was written, some people already knew that the earth is not flat. But, NOT everybody knew about that. So some part of the bible will tell you that the earth is round, and other part will tell you that it is not.
Personally, I don't believe that the scientific accuracy of the bible is important in understanding the true message of that particular book. Of course, GOD knows that the earth is not flat. But since His message is not about science, and it is delivered through divine inspirations (not words for words), it was up to the bible writer to put it in written form.