Has been discussed before. Might be worth searching for it. But basically, tactics wont help a keeper with movement based stuff, but it might help him stay in position better. Especially as some keepers can wander out of goal at times.
Have a keeper that was tactic 8, he does not have the roaming attribute but tense to leave the penalty box. After I up to 10, the roaming is lesser. I'm not that sure how much this will affect the roaming (or maybe I made a wrong observation)
I must say that I almost never saw a player take advantege of the goalkeeper wandering around. Somtimes I even saw strikers alone in the penalty box while the keeper was far away and instead of getting an easy goal they passed the ball back or just waited for the goalkeeper to come back.
I have a roaming Keeper who is sometimes crosses the half. Been trying to train his tactics or maybe start playing him in the outfield. But he's only 1.5 stars so I might sack him.
If he has roaming special ability, then I don't think tactics will help much. You might be better off retraining him as a defender or selling him next trade period - you should find a bot willing to buy him.