It is not possible to answer the question without information about the number of significant figures required.
12,437 rounded to four significant figures = 12,440
5 of them.
It is 6.7 when rounded to 2 significant figures
You didn't say how many significant figures. But, rounded to six significant figures it would be 5206.00
At least 1 and at most 7. It could be 3,999,999.9 rounded to 7 significant figures; It could be 3,999,999 rounded to 6 significant figures; It could be 4,000,015 rounded to 5 significant figures; It could be 4,000,429 rounded to 4 significant figures; It could be 3,999,999 rounded to 3 significant figures; It could be 4,049,999 rounded to 2 significant figures; It could be 4,492,467 rounded to 1 significant figure.
0.00721004 rounded into three significant figures is 0.00721
0.000709999 rounded to 3 significant figures is 0.000710
44.981 rounded to three significant figures is 45.0
16.275 rounded to 3 significant figures is 16.3
79,966.92 rounded to three significant figures is 8.00e4
34,696 rounded to two significant figures is 35,000.
9,682 rounded to three significant figures is 9,680.