@BOAC
As written you are probably correct that I7 should read 99 if you want 98.99 to be multiplied by 1.2 but 99.00 not to be multiplied. In using 100 I did make the heroic and possibly erroneous assumption that 99 included values up to 99.99 (and just for completeness because I assume we are working with money I am only quoting to 2 decimal places - the formula will actually work to the 15 decimal places to which excel calculates).
On your second query I read Bigwings original request 'multiply the amount by... as show the total rather than show the increase which is what using the decimals on their own would produce.
@Bigwing
Just a further thought that if you are going to copy my formula down a column then you need to use absolute references to the table ie:
=A8*INDEX($J$3:$J$7,MATCH(A8,$I$3:$I$7,1),1)
All the best
EG