Witholding tax can't auto calculated when generate in IDR currency

Dear Expert,

currently, i'm facing some problem of auto calculated witholding tax.

this tax accounted when invoicing, and we have tested in 3 currency (SGD, IDR, USD). tax rate 2.5%.

let's say all the amount are same = 100,000

below are journal after testing

for USD & SGD :

dr Expense 100,000

cr vendor 97,500

cr Tax 2,500

for IDR :

dr Expense 100,000

cr vendor 97,503

cr Tax 2,497

amount of tax, should be all same (2,500)

should not be currency translation issue / rounding problem.

please advice

many thanks for your help