Yes, that looks like a job for a lookup table:

Input  Output
-----  ------
0      1234.0
1      1234.5
2      1235.0
3      1235.5
4      1236.0
5      1236.5

You could simplify it slightly, as the LSB (Least Significant Bit) of your input is just switching between ".5" and ".0" so the lookup table only really needs to handle the other (7?) bits.