I disagree. I think an American would be as likely to say “three and a half bucks” as “three fifty,” in context.
At least this thread helps me understand Sherlock Holmes stories a bit better.
Those aren’t denominations of currency. They’re just numbers. Just like “million” can be a number designating how many dollars are under discussion. But “dollar” is the denomination of currency and “million” is a number or amount.
Basically true, but it would be pronounced more like tree-fiddy.
You may find this of interest.