2.58 rounded to 1 significant figure is 3. 2.3 rounded to one significant figure is 2 and 10^-2 is 0.01, which is the same if you round it to one significant figure. This is because when the first number that ISN'T a 0, you round it either up or down to 1 significant figure, and in this case, it is 0.01.
5.68 rounded to one significant figure is 6. 10 to the power of three is 1000, and 1000 doesn't need to be rounded to one significant figure. 3 x 0.01 is 0.03, and 2 x 1000 is 2000. 2000 x 0.03 is 60. 6 x 1000 is 6000. then you divide 60 by 6000, which is 0.01.
