A few quotes from the Rabbi on 'Tzedakah and Healing'
in which he teaches that one who lingers and keeps a counterfeit coin in his possession passes the Ne'ilah prayer in transgression.
Whoever lingers in keeping a short weight or measure in his home or shop transgresses, as it says: "You shall not have in your pouch alternate weights, larger and smaller". One is still transgressing even if one does not ever measure according to it, and this transgression remains in effect even during the Yom Kippur Ne'ilah prayer. This is the rule for similar cases – not to delay in getting rid of a paid bill. Nor should one delay with a silver-plated copper coin and the like.
Likutei Khemed, Part One, Rules on Weights and Theft, and False Pretense, Halakhot 1-3, pp. 131-132, Hapoel Hamizrachi Press, 1976
