Macbeth "sees" a dagger before murdering Duncan, and "hears" a voice after it. Do these details tell us anything about his attitude to murder?

They definitely do. While much attention often focuses on Macbeth's murderous rampage and subsequent demise, it's sometimes easy to forget he is initially reluctant to commit acts of of violence. This reluctance is made manifest by the fact that Macbeth's evil deeds seem to unhinge him. As you note in your question, Macbeth imagines a dagger before killing Duncan, and hears an imagined voice afterward. These strange hallucinations suggest that both the prospect of murdering an ally, along with actually following through with this act, are entirely unsavory, so Macbeth's mind is accordingly wracked with guilt. As such, based on these details in the play, we can surmise that Macbeth's attitude toward murder is one of disgust, apprehension, and dread, as his mind can't seem to handle the stress of murdering a former friend in cold blood.