See L. Y. Rahmani, “Jewish Rock-Cut Tombs in Jerusalem”, Atiqot III (1961), p. 119 and note 6. Here he traces the practice of placing coins in tombs to a Greco-Roman belief, whereby a coin was placed in the mouth of the deceased in order to pay Charon for conveying his shade across the Styx. However, Jews looked upon the custom of placing coins in tombs as idolatrous.