In D&D 5e, spell save DCs can be any number based on the calculation (Player's Basic Rules pp. 22, 30):
Spell save DC = 8 + your proficiency bonus + your Wisdom modifier
Spell save DC = 8 + your proficiency bonus + your Intelligence modifier
However, the DM screen has a table for setting skill DCs for tasks, which are all divisible by 5 (I don't have my screen to reference the exact figures).
Are there any reasons not to set task DCs to anything between these defined, round numbers?