For areas that don’t use 8.33 kHz channel spacing it’s simple - the last digit is just implied. For example if you tune 123.42 the radio will actually be on 123.425 - which is what you wanted. For 123.45 the radio will be on 123.450, which is also what you wanted it to do. So far so good.
For areas that use 8.33 kHz channel spacing you will have to use your pilot client to tune the radio. You can check How to tune 8.33 kHz Frequencies for the details.