Rounding whole numbers is not a difficult concept to learn once you know your whole number place values. The digit to the farthest right in a whole number is in the one's place, and for each place you move to the left, the place value multiplies by 10.
The second digit to the right is in the 10's place, the third is in the 100's place and the pattern continues. The first thing you need to know about rounding is to what place value you are rounding. Take the number 1,857. To round this number to the nearest 100's value, find the digit in the 100's place. It is eight. Find the digit to the immediate right. If its value is four or less, the eight remains an eight, and the numbers to the right all become zeros. If the value of the digit is five or higher, the eight becomes nine, and the numbers to the right become zeros. The number 1,857 rounds to 1,900.