How to set lower precision only for "view"

[lain]

I am trying to implement a table widget which displays (real) numbers.
I want to display data in the table with lower precision (say, number
of digits after the decimal point is 2) without reducing the actual presicion of the referenced data.
I thought that I can store the rounded and not-rounded data separately as
DisplayRole and EditRole, respectively, but it turns out not true
as far as looking at the sources of QStandardItemModel::setData() and
QTableWidgetItem::setData().

void QStandardItem::setData(const QVariant &value, int role)
{
    Q_D(QStandardItem);
    role = (role == Qt::EditRole) ? Qt::DisplayRole : role;
    .......
}

void QStandardItem::setData(const QVariant &value, int role)
{
    Q_D(QStandardItem);
    role = (role == Qt::EditRole) ? Qt::DisplayRole : role;
    .......
}

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Should I prepare another instance of StandardItemModel or my own container to store unrounded data?