Is 'each' obligatory?

[Winwin2011]

There are three robots on the shelf in a toy shop.

Customer: How much are the robots?
Shop assistant: They are one hundred dollars./They are one hundred dollars each.

Are they both natural in the dialogue of the Shop assistant? Is 'each' obligatory?

Thanks.

 

[Tdol]

Each is not obligatory.

 

[sergeyrais]

I guess without each

one hundred dollars can be understood as the price for all three robots on the shelf in the toy shop.​

 

[5jj]

I guess without each

one hundred dollars can be understood as the price for all three robots on the shelf in the toy shop.​

It's unlikely.

 

[Tdol]

I guess without each

one hundred dollars can be understood as the price for all three robots on the shelf in the toy shop.​

We generally go for the most obvious and probable meaning. The most likely meaning is that they cost that each. If we need clarification, we can always ask.