Rounding to the Nearest 5, but making 5 come back as 5 instead of 10

What does you get when you use N / 5

Please define what you're trying to do.

You said that you're using a custom calculation script. Based on what you posted your rounding up a number that is divided by 5, then you multply that result by 5.

Then in the examples below you're using substraction. And not only that is a subsctraction but you're also substracting a larger number from a smaller number; the larger number also has a negative value.  So you're ccreating a confusion here.

If all you need is to avoid the zeroes appearing to the right of the decimal point use the utilprintf() method and if you don't want anything to be rounded up , nand all you want is to truncate a number that has decimal value then use the toFixed() method.

For the util.printf() method you should use Something like this: 

event.value = util.printf("%.0f", event.target.value);

Whit that calculation they all will return 5.

To get results you want, you need something like this: Math.ceil(N/5)*X , X being field where you input first value (0.01, 5.01. 10.01...etc)