Elementary Mathematics, Part 1 gives the following guidelines:

Because a line plot is based on a number line, it must be drawn for grades K-3.

The values appear below the horizontal line, without the numeric indicator. The first digit of the value is aligned with the scale mark.

Arrows are on either end of the horizontal line as in print.

The label of the line plot is aligned with the first cell of the number line with no blank line between.

X's are not drawn. They are represented by the full cell.

I would highly encourage anyone brailling elementary mathematics to get copies of the workshop materials "Elementary Mathematics, Part 1" and "Elementary Mathematics Part 2" from the Professional Development Conference, April 3-5, 2008, Dallas, Texas. They cover almost everything you will find in elementary math texts with examples of the braille and the tactile drawings.