A vlookup table would work. And use an if statement to first test for
<80. Like this. Lets say the formula in the cell is:
=sum(101+3), which equals 104, but you want 108:

=IF(SUM(101+3<80),0,VLOOKUP(SUM(101+3),mylookuptab lerange,2,FALSE))

The mylookuptablerange might be a lookup table like this:
A B
80 80
81 81
82 82
100 100
101 102
102 104
103 106
104 108
105 110

Do you follow?