Hi there!
First of all we're going to look at all the numbers in their places in 845,001.
1 is in the ones place
The zero beside the 1 is in the tens place
The next zero is in the hundreds place
5 is in the thousands place
4 is in the ten-thousands place
And 8 is in the hundred-thousands place.
Now, let's look at 8 for now. We see it's in the hundred-thousands place.
In order to round this particular number we look at the number beside it (to the right)
What would make this really easy is if you remember the term,
5 or more, raise the score
4 or less, let it rest
So if the number beside the 8 is 4 or less, round down, but if it were bigger, you'd round the number up.
Look! In our case there is a 4 next to the 8 which means to round down...
So 845,001 rounded to the nearest hundred thousand is 800,000.
Hope this helps! <3