Square Rounding Error (Banker's Rounding) - square-connect

Question

I'm getting an error from square that says
{"errors": [{"code": "BAD_REQUEST","detail": "The total of the requested payments does not match the total of the sale order.","category": "INVALID_REQUEST_ERROR"}]}
The item is 3.00, the tax is 9.5% and our app fee is 3%.
On my end I send over
3.00
+ 0.29 (0.095 * 3.00 = 28.5 rounded up)
+ 0.09
______
3.38
I can clearly see that this is the amount I'm sending in the request and it works if the item is priced at 2.99 or 3.01. When Square responds to the create order it returns $0.28 as the tax amount, which is not Banker's rounding. In this situation is best for me to assume that Square will not fix this error and I should round down taxes?
RESPONSE from order endpoint:
{"order": {"id": "gMTUBc5FrYvLzkoNv6xOYfkLtkUZY","location_id": "RE7KBN4EGW4KT","line_items": [{"uid": "Z3mT3QHmkk4SPCkbrSW5MB","catalog_object_id": "NN5CHF66YK6MUGXG3BNWF6X5","quantity": "1","name": "Steamer","variation_name": "Regular","base_price_money": {"amount": 300,"currency": "USD"},"taxes": [{"uid": "rQurMfiksaO3xTaMqWdb1C","catalog_object_id": "YSI7WUNXGGSJRQEQ4QEQYK5G","name": "Sales Tax","percentage": "9.5","type": "ADDITIVE","applied_money": {"amount": 28,"currency": "USD"},"scope": "LINE_ITEM"}],"gross_sales_money": {"amount": 300,"currency": "USD"},"total_tax_money": {"amount": 28,"currency": "USD"},"total_discount_money": {"amount": 0,"currency": "USD"},"total_money": {"amount": 328,"currency": "USD"},"variation_total_price_money": {"amount": 300,"currency": "USD"},"applied_taxes": [{"uid": "rQurMfiksaO3xTaMqWdb1C","tax_uid": "rQurMfiksaO3xTaMqWdb1C","applied_money": {"amount": 28,"currency": "USD"}}]}],"taxes": [{"uid": "rQurMfiksaO3xTaMqWdb1C","catalog_object_id": "YSI7WUNXGGSJRQEQ4QEQYK5G","name": "Sales Tax","percentage": "9.5","type": "ADDITIVE","applied_money": {"amount": 28,"currency": "USD"},"scope": "LINE_ITEM"}],"fulfillments": [{"uid": "jJtsXtwaWfjJBIpbe7wkk","type": "PICKUP","state": "PROPOSED","pickup_details": {"pickup_at": "2020-06-14T20:58:09.257Z","recipient": {"display_name": "Table: #1"}}}],"created_at": "2020-06-14T20:43:09.731Z","updated_at": "2020-06-14T20:43:09.731Z","state": "OPEN","version": 1,"total_tax_money": {"amount": 28,"currency": "USD"},"total_discount_money": {"amount": 0,"currency": "USD"},"total_tip_money": {"amount": 0,"currency": "USD"},"total_money": {"amount": 337,"currency": "USD"},"service_charges": [{"uid": "2lD47tU2idwjyOpydkfrtB","name": "Service Fee","amount_money": {"amount": 9,"currency": "USD"},"applied_money": {"amount": 9,"currency": "USD"},"calculation_phase": "SUBTOTAL_PHASE","taxable": false,"total_money": {"amount": 9,"currency": "USD"},"total_tax_money": {"amount": 0,"currency": "USD"}}],"total_service_charge_money": {"amount": 9,"currency": "USD"},"net_amounts": {"total_money": {"amount": 337,"currency": "USD"},"tax_money": {"amount": 28,"currency": "USD"},"discount_money": {"amount": 0,"currency": "USD"},"tip_money": {"amount": 0,"currency": "USD"},"service_charge_money": {"amount": 9,"currency": "USD"}},"source": {"name": "Table: #1"}}}

Answer 1

Banker's rounding only applies when the ending number is equidistant between two numbers (in this case, .05).
In your example:
3.00
+ 0.28 (0.095 * 3.00 = 0.285 which according to Banker's rounding, rounds to the closest even number, so this would be 0.28)
+ 0.09
_______
3.37
In your other example (3.01):
3.01
+ 0.29 (0.095 * 3.01 = 0.28595 which would round to 0.286 and then use normal rounding, since it doesn't end in 5, to be 0.29)
+ 0.09
______
3.39