All dates are transcribed in figures.
When the ordinal is added to a date when said -- ...on May 5th... -- it is not good grammar. It is not correct to say the month and date and add the ordinal to the date. Whether you are going to transcribe it with the ordinal depends on how "verbatim" you are going to be.
When the month is not said, the ordinal, of course, is correct.
...on the 5th of May...
...came on the 5th...
...on May the 5th...
Happy punctuating!
Margie