It is written..."For sin shall not have dominion over you: for ye are not under the law, but under grace." (Rom 6:14)
Sin still has dominion over those under the Law.
The way you are interpreting this verse you are calling the law sin.
This would be the proper interpretation:
The law of sin shall not have dominion over you because with grace you are not under the law of sin and death.
Law of sin:
Rom 3:23
23 For all have sinned, and come short of the glory of God;
Law of sin and death:
Rom 3:20,21
20 For when ye were the servants of sin, ye were free from righteousness.
21 What fruit had ye then in those things whereof ye are now ashamed? for the end of those things is death.
Sin had dominion over everyone before God's gift of salvation.
It wasn't the law that gave sin dominion over everyone.
The law only defines what sin is.
As a believer we are not under the law. (Of sin) and the law (of sin and death).