Unless you're specifically rounding the result in the formula, Excel
does not perform any rounding. It does, however, present them onscreen
in a variety of formats. For instance, if your formula is =1/3, the
result is 0.333333333333333333 with the 3 recurring, and Excel is
cognizant of all those recurring threes. What is displayed on screen
depends on how the cell is formatted, whether as a single digit, or
currency, or a fraction, or what. So the answer to your question is
likely to be: from the menu, click Format Cells and select the way
you'd like Excel to present that particular cell.