How do I override tax information in a NetSuite sales order POST request?

Question

From a third-party app, I'm trying to report an order as a sales order to NetSuite via the API.

Basic sales order creation can be done through the following API URL https://{{\_.app_id}}.suitetalk.api.netsuite.com/services/rest/record/v1/salesOrder

I want to be able to supply the taxTotal and total fields found in the documentation, but when I include them in the POST json they are not applied to the sales order. I need the tax to be applied at the order level and not on a per item basis.

Documentation https://system.netsuite.com/help/helpcenter/en_US/APIs/REST_API_Browser/record/v1/2023.2/index.html#/definitions/salesOrder

I've tried to format the JSON for the POST request like so

{
    "department": {
        "id": "9"
    },
    "custbody_cta_shipping_status": {
        "id": "1"
    },
    "entity": {
        "id": "1234",
        "refName": "test"
    },
    "item": {
        "items": [
            {
                "amount": 20,
                "item": {
                    "id": "5576"
                },
                "quantity": 3
            }
        ]
    },
 "billingAddress" : {
    "addr1": "test address 1",
    "addr2": "test unit",
    "addrPhone": "123-4567",
    "addressee": "test testperson",
    "city": "test city",
     "country" : {
            "id": "US"
        },
     "state": "NC",
     "zip": "12345"
 },
 "shippingAddress" : {
    "addr1": "test address 1",
    "addr2": "test unit",
    "addrPhone": "123-4567",
    "addressee": "test testperson",
    "city": "test city",
     "country" : {
            "id": "US"
        },
     "state": "NC",
     "zip": "28203"
 },
    "total": 200,
    "taxTotal": 10
}

I was expecting the the total to be 200 and a taxTotal field when I run the get response for the order but what I get is the following

    "subtotal": 20.0,
    "suppressUserEventsAndEmails": "F",
    "toBeEmailed": false,
    "toBeFaxed": false,
    "toBePrinted": false,
    "total": 20.0,
    "totalCostEstimate": 18.0,
    "tranDate": ****,
    "tranId": ****,
    "updateDropshipOrderQty": "T",
    "webStore": "F"

the total seems to be ignoring the value I passed in for total and there is no taxTotal in the response.