Weird problem

Ok so I have an entry in the database that sets the discount of a
product, and I have it as a decimal.
Here is what I used when I created the table:

t.column :discount, :decimal, :precision => 3, :scale => 2, :default =>
0

However, when I create a new product and add the discount to like 10.0%
it always comes out as 9.99. Does anyone know why it is doing this?