Rounding to the nearest hundred, so the deciding digit is the tens digit and everything to its right - tens and ones - becomes zero. Numbers reach four digits, so the answer keeps a thousands digit that never changes and a hundreds digit that sometimes carries.
The carry is the part worth watching: 3,960 to the nearest hundred is 4,000, not 3,900 - rounding the hundreds digit up from 9 rolls it into the thousands. A page of these makes that case come up on its own rather than as a footnote.
Look at the tens digit. 5 or more rounds the hundreds digit up; 4 or less leaves it. Then set the tens and ones to zero.
The tens digit is 6, so the hundreds digit rounds up. But the hundreds digit is 9, and 9 plus 1 carries into the thousands - so 3,900 becomes 4,000.
The tens digit is 5, so it rounds up: 2,800. Numbers ending in exactly 50 land on each sheet on purpose, because half-way cases are the ones students hesitate on.
Turn on Include Answer Pages and a matching key prints behind each worksheet page, with the questions in the same order.