As BrenBarn stated, tracking fractional transactions beyond 8 decimal places makes no sense in the context of standard stock and mutual fund transactions. This is because even for the most expensive equities, those fractional shares would still not be worth whole cent amounts, even for account balances in the hundreds of thousands of dollars.
One important thing to remember is that when dealing with equities the total cost, number of shares, and share price are all 3 components of the same value. Thus if you take 2 of those values, you can always calculate the third: (price * shares = cost, cost / price = shares, etc). What you're seeing in your account (9 decimal places) is probably the result of dividing uneven values (such as $9.37 invested in a commodity which trades for $235.11, results in 0.03985368550891072264046616477394 shares). Most brokerages will round this value off somewhere, yours just happens to include more decimal places than your financial software allows.
Since your brokerage is the one who has the definitive total for your account balance, the only real solution is to round up or down, whichever keeps your total balance in the software in line with the balance shown online.