You are probably rounding up or down.
This is from Access help
The default type of Number is a "Long Integer" - which IS
an integer,
that is, a whole number.
Rounds a number to a specified number of digits.
Syntax
ROUND(number,num_digits)
Number is the number you want to round.
Num_digits is the number of digits you want to round to.
Negative rounds to the left of the decimal point; 0 (zero)
rounds to the nearest integer.
_____________
ROUNDDOWN
Rounds a number down, toward 0 (zero).
If this function returns the #NAME? error value, you may
need to install msowcf.dll.
Syntax
ROUNDDOWN(number,num_digits)
Number is any real number that you want rounded down.
Num_digits is the number of digits you want to round to.
Negative rounds to the left of the decimal point; 0 (zero)
or omitted rounds to the nearest integer.
___________
ROUNDUP
Rounds a number up, away from 0 (zero).
If this function returns the #NAME? error value, you may
need to install msowcf.dll.
Syntax
ROUNDUP(number,num_digits)
Number is any real number that you want rounded up.
Num_digits is the number of digits you want to round to.
Negative rounds to the left of the decimal point; 0 (zero)
or omitted rounds to the nearest integer.
Jim