فَإِنْ خَافُوا أَنْ يَنْتَشِرَ الْكَفَنُ عَنْهُ: عَقَدُوهُ
Translation: If there is concern that the shroud may come open, it may be tied.
Yantashira al-kafan means that the shroud may loosen or open. The permitted tie is a practical way to secure the covering, not a separate act of worship.
The text conditions tying on the possibility of unwrapping; a secure shroud does not depend upon extra knots.