Actually, it is possible for a teacher to grade assignments as decimal number such as 10.5.
We do a similar thing in our courses. In Polish universities the most often used grading scale is 2.0 (fail) - 3.0 (satisfactory) - 3.5 (satisfactory+) - 4.0 (good) - 4.5 (good+) - 5.0 (very good). I created a custom scale with the following grades: 2.0, 3.0, 3.5, 4.0, 4.5 and 5.0. The fact that makes it easy for us is that we don't use fractions other than halves. However, the problem in our case was that in the Polish scale 2.5 is not given (a fail is a fail, as simple as that
), which would distort the averages a little, so we actually included 2.5, but our instructors simply don't award this grade.
Similarly, you could create a custom scale with decimal points, but - of course - this is feasible only if you are planning to use low numbers, because if you wanted to have a scale from 0 to 10, with decimals, you'd actually have to create a scale with 101 entries. Imagine what you'd have to do, if you wanted to have a scale from 0 to 100 with all decimals