[Grammar] Tense

[Raymott]

Originally Posted by Hiro

Some people argue that habitual things should be included in the exceptional sequence: The man said that he goes to church every Sunday. We reject this use because ...

In giving this rule, your grammar book admits that not everyone would agree, but that this was the opinion of their editorial team.
I would not interpret this as being told that you "have to" do this in English.
"You "have to" add an /s/ on the present tense of a verb when used in the third person." That's a "have to" rule in Standard English.