How is 305 rounded to the nearest 10
305 is equally close to 300 and 310.
When we are rounding to the nearest ten, we do in the flowing fashion.
(i) If a number ends in 1, 2, 3, or 4, then round down
(ii) If a number ends in 5, 6, 7, 8 or 9, then round up.
Thus, 305 can be rounded to the nearest ten as 310.
Hope it is clear to you now,