A currency validator with a cash cassette for use in vending machines has an acceptor module for receiving various sizes and denominations of currency, a sensor which confirms the validity of the currency and a drive unit which transfers the currency to a stacker mechanism for inserting the currency into a cassette cash box that is securable and tamper resistant. The currency validator also has a screw drive mechanism operative with the stacker wherein the screw drive mechanism controls the movement of the stacker to insert the currency into the cassette cash box. A processor controls the stroke or movement of the stacker mechanism depending upon the size of the currency inserted into the currency validator. Moreover, the cassette cash box is structured such that the stacker is included within the cassette cash box and is operatively controlled by the rotation and movement of the screw drive mechanism which may also be included in the cash cassette. The cassette cash box is detachably mounted within the currency validator housing and is easily exchanged with an empty cassette cash box so as to reduce the downtime of the vending machine which is connected to the currency validator.