Pfthb

Half a pence for my domain,

On a face I can be found,

Keep me and appear quite sane,

Green and growing on the ground,

Or in a basket with my friends,

A block of wood behind,

Where all of us had met our ends,

The verdict was unkind.

What am I?

I guess the answer is

Head

First lines
Half a pence for my domain,
On a face I can be found,

These refer to a coin, where a head appears on one face (half the coin), and strangely, the head being on a face (not the other way round) is a riddle too.

Next line
Keep me and appear quite sane,

You must keep your head, not lose it.

Next line
Green and growing on the ground,

A mass or carpet of flowers is a head.

The last four lines refer to the

French Revolution when non-citizens where beheaded.

I believe that you are referring to

Monarchy

Half a pence for my domain,
On a face I can be found,

The crown is on one face of the coin, specifically a coin that only existed within a monarchy, too.

Keep me and appear quite sane,

The Brits still seem (mostly) sane and they still have a monarchy in place.

Green and growing on the ground,

Or in a basket with my friends,
A block of wood behind,
Where all of us had met our ends,
The verdict was unkind

Ah, the infamous French revolution where poor King Louis XVI and Marie Antoinette, along with many other aristocrats, had their heads separated from their bodies and dropped in a basket. And like their bodies, the heads of state were no more and the body - the bourgeoisie - existed independently of the monarchy, throwing it away in the wastebasket of history. Vive la revolution!

Okay, another answer. This one should incorporate your title a little better, but not your comment on my previous answer... sigh.

Golf ball

What's if all fore?

Dunno about the 'if' misspelling, but 'fore' is a warning to people about to get pegged by a ball.

Half a pence for my domain,

On a face I can be found,

The old golfers' habit of using coins to save their ball's location on the course.

Keep me and appear quite sane,
Green and growing on the ground,

Nobody wants to lose their balls as they play. Alternatively, this could refer to 'sane' being 'good golfer' and they keep their balls within the area of the course that is only composed of growing grass, and perhaps even make it to the 'green'. They're not taking 'insane' shots into sand traps or the woods or water.

Or in a basket with my friends,

The golf balls are carried around in baskets together.

A block of wood behind,

Where all of us had met our ends,

A block can refer to an area, so perhaps these golf balls are lost in the woods?

The verdict was unkind.

The aforementioned golf balls were lost in the woods and were never found, or the golfer gained points on the hole from not meeting par requirements.

Are you:

A flower?

Green and growing on the ground

Flower's stems growing in the ground

Or in a basket with my friends

Or in a plant pot/hanging basket

A block of wood behind
Where all of us had met our ends
The verdict was unkind

Something to do with plucked flowers slowly dying?