I would use tending to in the following way: I am tending to (caring for) this garden, I am tending to (looking after) the store I am tending to my daughter (caring for) she has been ill I would use attending to in the following way: He is attending to the matter. There may be two people arguing and someone is charge is sent to attend to (sort out) the matter. Go and attend to those customers. Many people are waiting in a store to be served someone in charge sends someone to serve (attend to) them.

Tending to something means you're dealing with/paying attention to something or someone. So if you "tend to the sick" it means you look after sick people and help them feel better. If you "tend to the fire" it means you check on the fire and make sure its not burning out. Tend can also be used to mean 'tendency'. For example "he tends to go home early" means he has a tendency to go home early; he does it often and people expect it of him.