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