Rounding tax amount for Paypal - paypal

Question

In a US e-commerce webshop I am looking for input on how to solve an issue with Paypal Orders API
Example
The price per lamp excluding tax is $1547
A customer adds 2 of these lamps to his shopping basket
A third party service will calculate the tax amount for the two lamps to be $274.59
The total price for 2 lamps including tax is
2*1547 + 274.59 = $3368.59
When paying using Paypal we need to send the different amounts to Paypal Orders API.
This is where the issue occur with the tax amount.
Paypal want's it "pr unit", meaning 274.59 / 2 = $137.295
But Paypal will only accept 2 digits :-(
Below is how the order should be sent if 3 digits was allowed:
"purchase_units": [{
"amount": {
"currency_code": "USD",
"value": "3368.59",
"breakdown": {
"item_total": {
"currency_code": "USD",
"value": "3094"
},
"tax_total": {
"currency_code": "USD",
"value": "274.59"
}
}
},
"items": [{
"name": "Oval lamp",
"tax": {
"currency_code": "USD",
"value": "137.295"
},
"unit_amount": {
"currency_code": "USD",
"value": "1547"
},
"quantity": "2"
}
]]
This will give me an error:
"details": [
{
"field": "/purchase_units/0item/0/tax/value",
"value": "137.295",
"issue": "DECIMAL_PRECISION",
"description": "If the currency supports decimals, only two decimal place precision is supported."
}
]
If I then round the tax from $137.295 to $137.30 I get this error:
"details": [
{
"field": "/purchase_units/0/amount/breakdown/tax_total/value",
"value": "274.59",
"issue": "TAX_TOTAL_MISMATCH",
"description": "Should equal sum of (tax * quantity) across all items for a given purchase_unit"
}
]
If I update the total tax amount from 274.59 to 274.6 I get this error:
"details": [
{
"field": "/purchase_units/0/amount/value",
"value": "3368.59",
"issue": "AMOUNT_MISMATCH",
"description": "Should equal item_total + tax_total + shipping + handling + insurance - shipping_discount - discount."
}
]
My only option now is to change the total amount from $3368.59 to $3368.6, but that is not correct!
Any input is appreciated

Answer 1

Not much to say here--your question has the solution. Calculate the tax per item, round up or down as appropriate, and you'll have a different tax total. Use that.
If you want to adjust the order total to some different calculation, you'll need to add another line item with the positive or negative amount.