Bob:
Here is the 1855 Griffiths Valuation head of household listing for Taghboy civil parish. There are eight Rogerson entries including a Thomas in Taghboy. I would assume that this is your Ggrandfather.
http://www.failteromhat.com/griffiths/roscommon/taghboy.htm
You can use www.askaboutireland.ie to search the Griffiths and get a better idea where the farm may have been located.
I checked the online Irish phonebook and there are two Rogerson entries in Ballforan. Here is the link. Make sure you hit the Resedential Tab. http://www.eircomphonebook.ie/#
Because of our privacy rules, we don't provide the info directly.
I found this record in the 1901 census. Not sure if this is your great-uncle.
http://www.census.nationalarchives.ie/pages/1901/Roscommon/Turrock/Cron…
You did not provide the name of the daughter who married the Murray so I did not find her in the census records. Whta year were Delia and Tommie born?
Let me know what questions you have,
Roger McDonnell