We look at the last digit to keep
Increase it by 1 if the next digit is 5 or more (this is called rounding up)
Leave it the same if the next digit is less than 5 (this is called rounding down).
We have 5,812
Look at digit of thousand. It's 5. Next digit is 8 ≥ 5. Therefore digit of thousand increase by 1.
Answer: 6,000