"I have 80 cents."
Chinese currency is divisible by 10, not by 100 like say Canadian Dollars. If you go into a store you will never see anything marked as say, 9.99 because there is no division beyond the 10s; instead you would see 9.9. It's wrong to call 毛 dimes because that implies further division is possible.
Unfortunately thst makes no more sense than '八块毛', or in English, a phrase like '5 dollars cents'.
We're mostly used to currency that has two units: the main unit, and a hundredth of that unit. In Chinese currency there are three, but just like dollars and cents they are different units, and it only makes sense to say the name of the unit if there are some.