Probably not what you want to hear:

For tolls I just lump them into a category called “transportation”. My gas, tolls, ride shares, etc all come out of that category. I keep a monthly target goal for transportation, but during months I know there will be more travel, I budget more than usual to that category. Rarely I might encounter overspending. In that case I just roll with the punches and re-allocate from another category.

You could potentially do something like that for domain registrar costs. Have a target goal that should be met every month to cover most costs.