Set up details for the taxes of a tax regime. Each separate tax in a tax regime includes records that are used to calculate and report on the tax, including:
Tax statuses
Tax rates
Tax rules

You can change the conversion rate type at invoice entry or payment creation time.
References:https://docs.oracle.com/cloud/latest/financialscs_gs/FAIPP/FAIPP1470345.htm

When you apply a prepayment to an invoice, the tax rate at the time of prepayment may differ from the tax rate at the time that the prepayment is applied to an invoice. Oracle Fusion Tax considers the tax calculated on the prepayment according to the value assigned to the Applied Amount Handling option in the tax record. The values are Recalculated and Prorated.
For example, you apply a prepayment amount of 5,000 USD to an invoice with a total amount of10,000 USD. At the time of prepayment, the applicable tax rate was 5% (250 USD tax on the prepayment); at the time of invoice creation, the applicable tax rate is 10%. Tax is calculated in this way:
* Recalculated: The tax is recalculated on the prepayment using the invoice tax rate and the same tax rate is applied to the invoice line amount. The tax calculation creates two tax lines: one for the invoice line amount and one for the prepayment with a negative amount. In the invoice example, the calculationcreates an invoice line amount tax line of 1,000 USD (10% * 10,000 USD) and a prepayment tax line of -500 USD (10% * -5000 USD). This reverses tax calculated on the invoice for the prepayment amount applied. The tax calculated on the prepayment is retained.
* Prorated:Etc.
References:https://docs.oracle.com/cloud/farel8/financialscs_gs/FAFTT/F1006655AN242EE.htm