In 1.16 Pre-release 5, the Rotation NBT tag does not seem to affect the rotation of an armor stand when placing it. It will face the player that placed it until it is teleported.

Replication:

Give yourself an armor stand with a specific rotation (This bug does not work when using the /summon command or a spawn egg that spawns an armor stand), like so:

/give @p minecraft:armor_stand{EntityTag:{Rotation:[0.0F,0.0F]}} 1

Then place the armor stand. The model will be looking towards you rather than the direction set by the Rotation tag. However, if you show hitboxes with F3+B, the blue line that shows where the armor stand is looking points in the direction set by the Rotation tag. Despite this, if you execute the following command, the armor stand will teleport in the direction the model is facing, and the blue line will point in that direction as well.

/execute as @e[type=minecraft:armor_stand] at @s run tp @s ^ ^ ^1