How to prevent Excel rounding numbers or adding redundant 0's?

crtl + ASelect all - right click - format cells - custom- ########.##################### will do what you want
It won't show leading or trailing zeros

If you already have a number in the cell then you can't change the format to text (...or you can but it doesn't work!). You can verify that - if data is in A1 then change format to text and use this formula in B1

=ISTEXT(A1)

The answer will be FALSE

You need to format the cells as text before you input the data - then the data will be displayed as entered

To format the column as text "after the fact" try this:

Select column of data then use

Data > Text to Columns > Next > Next > under "column data format" select "Text" > Finish

That should format the whole column as text and show the number of digits for each entry as entered.

Your problem is that you're formatting the numbers as text rather than number and you don't have enough decimal places showing so it has to round.
crtl + ASelect all - right click - format cells - number - change decimal places to however many you want to show and check use 1000 separator (,)