Hello Eve -- Thanks for your inquiry. This is the strongest possibility of meeting your specifications of a Chinese coin with a rosette at the center and a dragon with no inscriptions. It is a 20 cash coin from the Province of Chekiang along the east coast of China.
10 CASH: 26 mm diameter
20 CASH: 32 mm diameter
Both 10 and 20 cash denominations are worth about the same, as follows:
worn: $1 US dollar approximate catalog value
average circulated: $8
well preserved: $15
These are approximate values only. Collecting Chinese coins is becoming more and more popular and, when popularity increases, so does demand and price.
If you have a nice-looking example of this coin it is wise to seek out a knowledgeable collector or reputable coin dealer for an in-person appraisal. The coin catalogs show that there are variations of the 20 cash coin that can be quite valuable, but it takes more detailed study than can be accomplished on this CoinQuest forum.
If you have a Chekiang 20 cash which bears the inscription TAI CHING TI KUO, then the values shown above go way up, to $200 for a coin in average circulated condition.