Is it necessary to keep the trailing zeros when converting to scientific notation?

(Note: My use of ^ is to notate an exponent.)

eg. 3100.0 x 10^2

My answer was 3.1 x 10^5 however the correct answer was 3.1000 x 10^5

(Is it pertinent to keep the trailing zeros?)

Another example would be:

1000 x 10^-3

My answer was 1 however the correct answer was 1.000

(Is there a reason for this?)