Let's simply round the number first with round:

round(prop("Completed") / prop("Subtasks"))

It will look something like this:

That round up is too dramatic. Let's try using a workaround: (100 * x) / 100

round(100 * prop("Completed") / prop("Subtasks")) / 100

Rounding Numbers

Cool! Let's dive a little deeper. Suppose we want to always round the number down rather than to the nearest integer? For this use floor:

floor(100 * prop("Completed") / prop("Subtasks")) / 100

Always round the number up with ceil:

ceil(100 * prop("Completed") / prop("Subtasks")) / 100