Answer:
The second digit (3) is the hundredths, so look at the digit after it (4). Since it's less than 5, you don't round up and it stays the same, final answer being .63
Explanation:
Whenever you're rounding, look at the digit that's one to the right. For 0.634, you'd want to look at the thousandths, which is 4, and if it's less than 5, then you don't round up for 3, therefore it is only 0.63. However, if for example it was 0.635, since the digit to the right of 3 is 5(or above), the hundredths place digit (3) rounds up by one, making it 0.64.
For a simpler example, rounding 143 to the nearest TENS (being the 4), it would be 140 as the digit to the right (3) is less than 5. Hope this helps.