QPainter::drawPolyline() uses wrong rounding for fractional coordinates

#include <QWidget>
#include <QPainter>

class MyWidget : public QWidget
{
    Q_OBJECT

public:
    MyWidget(QWidget *parent = nullptr) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent*) override
    {
        QPainter painter(this);
        painter.setPen(QPen(Qt::black, 1));
        painter.drawPolyline( QPolygonF() << QPointF( 0, 0) << QPointF(10, 0) );
        painter.drawPolyline( QPolygonF() << QPointF(10, 1) << QPointF(20, 1) );
        painter.drawPolyline( QPolygonF() << QPointF( 0, 2) << QPointF(10, 2) );
        painter.drawPolyline( QPolygonF() << QPointF(10, 3) << QPointF(20, 3) );

        painter.setPen(QPen(Qt::green, 1));
        painter.drawPolyline( QPolygonF() << QPointF(10, 2.99) << QPointF(20, 2.99) );
    }
};