3.00 not 3 or 3.0, as including the 2 decimals indicates to what place the number was rounded.
300
The first figure after the decimal point is tenths, and the second is hundredths. In thids case the hundredths are 0, but the thousands are 7 and so the hundredths are rounded up to a 1.... giving a...
16, or if you like, 16.00. Don't confuse a hundredth (0.01) with a hundred (100).
As a whole number, 3490 is already rounded to the nearest hundredth.