The story I heard is you give a payment for a knife or sharp object so as not to cut your friendship.My grandma would give us knife too and ask for a penny. I think it was from the old country.
Give a penny for any sharp object so not to be cut by it or something . Many reasons
on the interweb. I guess like that salt thing maybe.
My mom gave us a meat carving set with a dime in the box. I still have dime in there 20 years later.