=ROUND(number,-3)
If you need to round a number to the nearest 1000, you can use the ROUND function and supply -3 for number of digits.
How this formula works
In the example, cell C6 contains this formula:
=ROUND(B6,-3)
The value in B6 is 1,234,567 and the result is 1,235,000.
With the ROUND function, negative numbers for the second argument round to the left of the decimal and positive numbers round to the right of the decimal.
In this case, by supplying -10, we are telling ROUND to round the number to the 3rd place on the left -- the 1000's place.