TallinnCard gives you 25% discount on short-term daily rentals. If you start your rental period before your TC expires, you're still entitled to the TC discount for the entire rental period, valid when driving anywhere in Estonia and the Baltics. 

You can always ask Hertz counter for special sightseeing routes in and near-by Tallinn. GPS Navigation is also available for getting around easley and finding best sights and points of intrest.