Rounded shoulders can really hurt posture, aesthetic appearance, strength gains and more. It may impact the cervical vertebrae (neck) causing significant discomfort and pain.
Working your rotator cuff muscles (Infraspinatus, Supraspinatus, Subscapularis and Teres minor) will help you stabilize the scapula, which will help prevent rounded shoulders. Also stretching your chest helps this process.
I always say walk with a proud chest (chest out shoulders back). By doing this it also gives you a stronger look (in my opinion).
It is also important that we continue to stretch our neck. Using diagonal stretching with rotation. Adding static stretching, PNF stretching and dynamic range of motion.