It doesn't make any difference either you call it bitcoin or bitcoins, the purpose would be the same but if you think grammatically then 10 bitcoins is the right word.
Sounds about right. Grammatically Bitcoins makes more sense, but ultimately it doesn't matter much in my opinion.I personally say 10 bitcoin. "Bitcoins" generally doesn't sit well on my tongue. And the other thing is that every time I see someone say "10 bitcoins" is when I read a person with broken English's post.
And saying that it doesnt sit well in your tounge doesnt mean it's correct. And people may post broken english but it doesnt mean the term they used in their sentence is wrong. There are instances that sentence structure maybe wrong but the singular / plural term of a word might be correct. There is 10 eggs (not use as collective noun) << this is broken english but 10 eggs is correct see my point?
(just kidding) 
