I'm writing a story, and I'd like to know if I can use "on" instead of "onto". Someone told me that it's accepted to use the word "on" instead of "onto".

For example:

I put the box on the table.

I hang the painting on the wall.

The cat jumped on the table.

Only the last one could naturally take "onto" but it's okay with "on," in my opinion. You could, I suppose, say you put the box onto the table, but I don't think it sounds natural, and you would not hang a painting "onto" the wall.