Using an oral syringe (available at drugstore, intended for measuring pediatric medications and such), measure 11.5ml of Rodinal, add water to make 300 ml.(posted 8167 days ago)There's no reason to carry the calculations out to more than three significant figures. 300/26 = 11.5, for all practical purposes. I'd expect that a quarter-degree's temperature change would cause more variation than that extra .03846153846 ml of developer.
Personally, I'd probably measure 300ml water, and add 12ml developer. That'd give 312ml total solution, but my measurements would all be nice round numbers.