The zā reading is the 'bundle / bind / wrap' cluster — etymologically a separate character
紮 (silk-radical) that was merged into
扎 in the 1956 simplification. Core list:
包扎 (bandage a wound, wrap up),
结扎 (medical ligation, e.g. tubal ligation),
扎带 (cable tie / zip tie). Also serves as a classifier —
一扎花 (a bunch of flowers),
一扎钱 (a bundle of cash).