Particle, execute and summon commands round co-ordinates to nearest block to the nearest block.

What I expected-
The particle command would spawn particles relative to my location.
What actually happened-
Particles were spawned relative to the center of the block I was standing in.
How to reproduce-
Stand on the edge of a block.
Use a particle command such as:
/particle heart ~ ~ ~ 0 0 0 0
Observe that the particles spawn in the center of the block, and not at your co-ordinates.