The smallest unit of currency in the US is $0.01 so price tags are only ever to two decimal places. You can't charge somebody six tenths of a penny. If you were talking about weight, however, you would just read the individual numbers. E.g. "The package weighs three point four five six kilos."

Never seen a price tag written that way. I would round up and say: three dollars fifty

If you’re talking about US dollars, we don’t write cost like this. We would only write $3.45 which is three dollars and forty- five cents.

Wouldn't you just say 3 dollars 4 hundred fifty-six cents? (is it even cents? lol)