I will tend my mother, who is ill.
I have to stay at home to tend my sick mother.
When we use it to mean "take care of" then it's just "tend".
I tend my child.
I tend bar. (I'm a bartender!)
I like to tend my garden.
We use "tend to" when we mean "deal with" or "attend to". I'm so busy at work I have no time to tend to my diary at home!
And of course, you're right that we also use "tend to" to mean that someone has the habit of doing something.