speadsheet, 2 changes to 5

operating system is XP professional
software is office 98
program is speadsheet
When I type the digit 2 in the ones or tenth place in a number, the digit 2 is changed to a five. The way I enter the number 82 is typing “=82-3”. The result is 85 shows up in the cell. This occurs when I open a new spreadsheet and immediately type the digit 2.
Has anyone seen this happen before?
Is there a way I could have set all new speadsheets to round, average or something?