var cashRegister = {

total: 0,

lastTransactionAmount: 0,

add: function(itemCost) {

    this.total += itemCost || 0;
    
    this.lastTransactionAmount = itemCost;
},

scan: function(item, quantity) {

    switch (item) {
    
    case "oranges": this.add(0.49 * quantity); break;
    
    case "candy": this.add(0.45 * quantity); break;
    
    case "peanuts": this.add(0.98 * quantity); break;
    
    case "cookies": this.add(1.00 * quantity); break;
    }
    
},

voidlastTransaction: function() {

    this.total = this.total - this.lastTransactionAmount;
}

};

cashRegister.scan(item, quantity);

console.log("Your total bill is " + cashRegister.total);