Rounded numbers can be easier to use and remember than exact numbers. When you round a number to the nearest 10,000, you are determining what multiple of 10,000 the number is closest to. For instance, the number 24,000 is closer to 20,000 than 30,000, so it rounds down to 20,000.
Find the number that is in the ten-thousands place. For instance, in the number 64,700, the number 6 is in the ten-thousands place.
Look at the number immediately to the right of the number in the ten-thousands place. In the number 64,700, you would look at the number 4.
Increase the number in the ten-thousands place by one if the number to the right of it is five or greater. Then change all numbers to the right of the ten-thousands place to zeros. For example, the number 87,500 would round up to 90,000.
Keep the number in the ten-thousands place the same if the number to the right is less than five, and change all of the numbers that follow to zeros. For example, the number 84,500 would round down to 80,000.
TL;DR (Too Long; Didn't Read)
You can probably round to the nearest 10,000 easily in your head. For instance, it is obvious that 53,000 is closer to 50,000 than 60,000, and it is easy to see that 57,000 is closer to 60,000 than 50,000.
Remember that fives round up even though they are in between values. The number 44,999 would round down to 40,000, but the number 45,000 would round up to 50,000.