You can sell any amount you’d like, but the smallest denomination we support is up to 5 decimal places. In fact, if the fraction is super small, there is a possibility that we won’t be able to execute the trade due to market movement.
For example, if the price of a stock drops at all, though, a $0.00001 sale could end up failing to execute. But that’s an edge case. or example if you are trying to sell a small fraction of a share and the market moves downward, the sale amount could be less than a penny which would cause the trade to be canceled.