Xtol is as sharp or sharper than Rodinal. If you don’t want it as smooth as full strength Xtol you can try diluting it. Or use additives with Rodinal. Potassium thiocyanate at 1.5g/L per litre to working developer in Rodinal gives as fine grain as Xtol, so you may want to try half that or a quarter. It can speed up development with some films though.
Another option is sodium sulphite 20g/L would be a fair bit finer but not full Xtol level. You could make a stock solution in a jug, and pour some out and add your Rodinal when you want to develop.