If you set the decimal places in columns I and J to zero, the result in your formula will also be zero decimal places. It will round the result to 0 decimals without needing to use the ROUND function. Both columns need to be the same or you'll get a lot more decimal places than you have now.
You have your ratios formatted different ways in your screeshot and I do not know which you prefer. Here are two possibilities:
=I5/J5&" : 1"
=I5/100&" : "&J5/100
In Excel, when you use ROUND it will format the result with the specified number of decimal places. In Numbers, the number of decimal places depends on the format(s) of the referenced cell(s). When the end result is a number, you can simply format the cell so it displays properly, but when the result text you cannot.
So another way to do it if you like the 5:1 kind of format is to create a custom format. The formula will be a simple numeric formula of =I5/J5 . The custom format will look like this: