Actually as of April first off peak is now 7.7 cents/KWh. But that does not take into consideration variable delivery and transmission costs and GST.
After variable delivery and GST the cost is actually about 12 cents/KWh for off peak.
To fully charge a 2016 - 2017 Volt costs about $2 off peak (2.4 cents per Km using EPA rated 85Km EV range). For a 2011-2015 Volt it's roughly a $1.60 (2.5 cents per Km using EPA rated 65Km EV range). Most people don't use a full battery charge during their commute so the best metric is to take the cost in cents per Km and multiply that by your typical daily commute.