As you can see, this roof requires a replacement.  The shingles have significant granule loss.  You can also see exposed nails. 

A tarp can help prevent leaks from getting into the house; however, a tarp on the roof should be a temporary fix to stop an emergency leak.  This is not a permanent fix. 

As you can see, this roof has significant granule loss, which can happen over time.  This roof is in dire need of being replaced.  Shingles have a life expectancy.  But as with most things, proper maintenance and care will help with the life of your roof.