Is there a way to make tapered lines in Sketch? I attached the way I do it in Illustrator as an example below.
I don't use Sketch, but it does have a Vector Tool for making Bezier curves somewhat similar to the Pen Tool in Illustrator.
To make a tapering line in Illustrator without using a stroke style/profile it's easy enough to make by simply using the Pen Tool, so the same should be possible in Sketch and virtually any vector image editor with a similar tool.
Remember to set the stroke to none, and the fill to black.
Here's an example made in Illustrator
There's a tutorial on youtube showing how to use the Vector Tool in Sketch here
The simplest way to create a tapered line in sketch is probably by creating an Oval with small height
If you want a "proper" tapered line or one that is not straight you are unfortunately left to do it yourself using the Vector Tool as has already been pointed out.