In USA GRONSKI but in Poland: GroĊski
http://ivona.com do use the proper Polish spelling.
It is ALL in pronounciation.
GRONISKA is the way an EI Foundation volunteer transcribed the surname.
Groniska, Agata Brzyna, Galicia 22 1884 1906 Is the dot for the I or is the surname GROMSKA or GRONSKA. It is in the eyes of the transcriber.
Groniski, Adam Lechnica, Galicia 44 1862 1906 view view view view view
Groniski, Jan Cicke 43 1860 1903
Groniski, Mendel 17 1888 1905
With only these 3 GRONISKI I take it as a transcriber error either done at the port of departure or arrival.