Price round is an option under the Price field (Price Conditions and more setting)

Below are the price round options:

We use this value as example 12.57
Below are the example according to the first option until the eight options

1. 12.57 -> 12.00

2. 12.57 -> 12.50

3. 12.57 -> 12.57

4. 12.57 -> 12.57

5. 12.57 -> 12.99

6. 12.57 -> 12.95

7. 12.57 -> 12.099

8. 12.57 -> 129.00