You can do the rounding portion via formula, but you cannot control how the number actually displays via formula without converting it to a string (by using the totext()
function and passing in a format string).
It's better to just choose a format style for your numeric field so you can continue to do summaries on it, etc. If you choose a format style and it displays "#########" then that means that your field is not big enough to display the number (CR does this to prevent unintentional clipping). You just need to increase the size of your fields.