Keystrokes used in the 65 Character line count is defined as follows:

Each time you strike a key be it spacebar, a character, or even the shifts and control buttons all count as a character towards the 65 character lines.

For example:

HELLO is only 5 keystrokes (even though its caps) because you press the SHIFT and H at the same time (one keystroke).

HELLO is 7 keystrokes because the CTRL B (to bold) then HELLO then CTRL B to unbold.

HELLO is 9 keystrokes because the CTRL U, CTRL B (to underline and bold) then Hello the CTRL U, CTRL B (to unbold and turn off underline).

Bold and Underline do affect line count.

Please see this article for a more in-depth analysis of how characters are counted in Nuance:

Character Counting Explanation