Every new version of Excel comes with new or updated functions. The 2019 version of Excel is no exception. One of the new functions is MROUND.
MROUND is a little different than other rounding functions, as you reference a cell with a number and tell it to give you the closest multiple requested by you. For example, if I tell the function to give me the closest multiple of 400, then when I place a 1 in the referenced cell, it will give me a zero. However, if I place 300 in the referenced cell, the function will populate a 400. If I place 500 in the referenced cell, I will get 400 as well; but if I place 700 in the referenced cell, I will get 800.
Check out this video to see how to set up the function and see how it works: