All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
It is valid to respond with what you mentioned. It was narrated that Anas ibn Maalik said,
“Usayd ibn Hudhayr Al-Ashhali, a representative of the Ansaar, came to the Prophet and informed him of a family among the Ansaar that was in need of help. The narrator mentioned that the Prophet had just distributed some food among the needy. He said: "We have just distributed all the food we have. When you hear about more coming, remind me of this family." The narrator added, "Then, some barley and dates from Khaybar were brought to the Prophet . The household of this Ansaari family consisted mostly of women. The Prophet distributed the food among the people and set aside a part of it for this family. He generously allocated a good portion to them. Upon that, Usayd ibn Khudhayr said, 'O Messenger of Allaah, Jazaak Allaah ‘anna atyab al-jazaa’ (may Allaah reward on our behalf with the best reward).' The Prophet replied, 'Wa antum fa jazakallaahu atyab (or khair) al-jazaa’ (and you too, may Allaah reward you with the best reward). Verily, I have always known you to be faithful observers of patience. You will see selfishness and easy living after me, so be patient and endure until you meet me at the Hawdh (Basin, Cistern).'” [Ibn Hibbaan - Al-Albaani graded it Saheeh (sound)]
However, one does not have to confine the response to this exact wording. One may respond with any other wording to the same effect, such as "Wa Jazaak (and may He reward you)," or "Wa 'Iyaak (and you too)" or the like.
Allaah Knows best.