Rounding numbers is a concept taught in the early to middle grades and unfortunately, it causes some difficulty for many students. Why? Because students confuse place value, which really just refers to the place or position of a number; each place has a value of 10 times the place to its right. In the number 111, the number to the far left is ten times the number to the right of it which is 10 times the number to the right of it which is worth 1.
When a student is asked to round 74,580 to the nearest ten thousand, they will often say 75,000 instead of 70,000. Or, likewise when asked to round 12,745 to the nearest thousand, they will often say it's 12,800 instead of 13,000. Why? Because their understanding of the value of each place is easily confused.
Lots of practice and teaching for understanding will help to solidfy the concept of place value. Here are some great worksheets to help.