How to validate decimal places in Postman?

How can I validate how many decimal places data has?

 "value": [
    {
        "cotacaoCompra": 4.08520,
        "cotacaoVenda": 4.08580,
        "dataHoraCotacao": "2019-10-22 13:10:34.471"
    }
]

I need to validate that "cotacaoCompra" has 4 decimal places.

How can I do it with Postman?

Please help me.