There are certain values in JForex-API which have minimum increments, like stop loss and take profit prices which have 0.1 pip minimum increments. Consider the following price rounding approach:

public void onStart(IContext context) throws JFException {
    this.engine = context.getEngine();
    this.history = context.getHistory();

    ITick tick = history.getLastTick(instrument);
    double slPrice = tick.getBid() - 0.0010001;
    engine.submitOrder("marketOrder", instrument, OrderCommand.BUY, 1, 0, 10, roundToPippette(slPrice, instrument), 0);
}

private static double roundToPippette(double amount, Instrument instrument) {
    return round(amount, instrument.getPipScale() + 1);
}

private static double round(double amount, int decimalPlaces) {
    return (new BigDecimal(amount)).setScale(decimalPlaces, BigDecimal.ROUND_HALF_UP).doubleValue();
}

RoundingSL.java

Replace the roundToPippette(slPrice, instrument) call with slPrice to see the necessity of the rounding in this case.