For the constant sum question, is there a way to restrict answers to be round numbers?

Hi,
I am having participants enter two numbers that add up to 100 using the "constant sum" question type. I want their responses to end with 0 only i.e. be multiples of 10 (0, 10, 20...). I cannot find a way to do that in the existing Qualtrics functions.
I tried using custom validation and restrict the answers to match 0, 10, 20, ..., 100, but in that case, the constant sum restriction no longer works.
Would I be able to achieve this via the regex code in the Custom Validation function?
Thank you!!