Praise be to Allah.It is not permitted, because Allah has forbidden it in the aayah (interpretation of the meaning):
". . . but do not help one another in sin and transgression. . ." [al-Maa'idah 5:2]
There is no doubt that by doing this work you are making it easy for the bank to deal in the haraam matter of ribaa using the programs that you have developed. May Allah help us and you to do the things that will please Him, and keep us away from the things that will earn His wrath. May Allah bless our Prophet Muhammad.