in this case the first figure that is significant is 4,
when we look after 4, we see 3 , so we do not have increases 4, we are going to leave it
0.043≈0.04 (your answer)
if after 4 you would see 5, 6, 7, 8,or 9
you would increase 4 by one, for example 0.047≈0.05