Rounding makes it simpler to communicate.
In general conversation, you are unlikely to use exact numbers when they are very large. Rather than saying there are 62,105 inhabitants in an area, for example, this would usually be rounded to 62,000.
Rounding makes it easier to understand distances
The distance from New York to Los Angeles is 3,944 kilometres. We would be likely to say the distance between New York and Los Angeles is 4,000 kilometres.