Total Outdoorsman: How to Whip Finish a Rope
Sure, you can use a lighter to melt the end of a rope, but then the diameter at the end...

Sure, you can use a lighter to melt the end of a rope, but then the diameter at the end of the rope will be larger than the rope itself. This will make tying good knots an issue.
Here’s a better technique: Whip finish your rope with some old fly line. Just make sure to keep those wraps tight!