The documentation says:
amount
The invoice amount. The rounding up method depends on the invoice currency.
github.com/QIWI-API/pull-payments-docs/blob/40d48cf0/_pull-payments-api_en.html.md#parameters
amount
Сумма, на которую выставляется счет. Способ округления зависит от валюты.
github.com/QIWI-API/pull-payments-docs/blob/40d48cf0/_pull-payments-api_ru.html.md#Параметры
But the documentation does not specify the rounding methods.