Expression rounding

[Scorpio11]

Can someone please tell me something that is irritating..

I have created a query where there is a simple iif formula, where 1 condition, amount from 1 cell is pulled, in, second condition brings in a different cell.

Now in both cells, the amounts being pulled in only have 2 decimals - i have checked. but the expression result has put in something like 12 decimals after it eg: my cell - 12.15, the expressions result is 12.150013513579613 - it is like the query is making numbers up for the heck of it - and to crown it off, the Round expression is impotent. The plethora of decimals remain. Formatting is good for a surface effect, however the decimals are starting to mess with formula further on.

Can someone please explain this to me or tell me what i am doing wrong with the rounding or the expression.

[orange]

Perhaps you could show us the expression that is so irritating.
Also and Dim statement or definitions for the fields/variables involved.

[Scorpio11]

Apologies for not posting a reply sooner....

The expression is as follows:

Cost: IIf([Type]="Purchase",[Amount]),[COS])

There is nothing else involved. The [Amount] and [COS] fields come from a table where I input data.