There is the phrase, "良い一日を," but it's not really used in Japanese! If you want to say something nice to someone whom you live with and is leaving your house (to go to school/work, etc.), you can say いったらっしゃい！ If you are working in customer service, you can simply say, ありがとうございました！

I completely agree with Ms. Goldie. You can also say ごきげんよう(Farewell!) instead of 良い一日を, but we Japanese really don't use these very formal phrases. As for 行ってらっしゃい, it is quite common and is often replaced with 気をつけて(Take care.／Be careful.) depending on the situation.