Fortunately for us we do not still use the Roman numeral system in common practice today. We use the Hindu system, which was transmitted to us through the Arabic world of the Middle Ages.
It is uncertain when exactly Hindu numerals first came to the Islamic world of the Middle Ages. The Brahmasphutasiddhanta mentioned above came to Baghdad in the year 776 CE, and was presented before the current Caliph al-Mansur. This book was then translated into Arabic
Two Muslim mathematicians contributed greatly to the use of Indian numerals: al-Khwarizmi of Persia and al-Kindi, both of whom worked in the first half of the 9th century CE.
Like the Hindus before them, Arabic mathematicians began to change the numerals as well as they were used over time. Before the development of the printing press, everything written had to be written by hand, and thus there was no universal uniformity. Scholars working far apart over long periods of time would eventually change the numerals even unknowingly but simply through change of handwriting.
Use of Indian numerals in the Muslim world was limited primarily to mathematicians, however. Muslim scientists and astronomers generally used the older Babylonian system of numerals. This was in fact still in use until modern times in the Arabic world. Merchants also used a different numeral system, similar to that of the Greeks and Hebrews.