Start by identifying how many digits of precision you need.
Because, even if we had infinite precision calculations, when displaying the data back to users, we're not going to be displaying 28 decimal places (unless you're doing sub-atomic physics maybe), so we will be rounding at some point for display
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability