fix: round off tax withholding amount (backport #45271)

[mergify]

Issue - The TCS Amount is not getting rounded off even though round_off_tax_amount is checked when the Charge Type is "On Net Total" or "On Previous Row Total".

Steps to Replicate:

• Create a Tax withholding category with "round_off_tax_amount" as checked and threshold limit as 1.
• Create a Customer and set the tax withholding category.
• Now create a Sales Invoice. TCS will be deducted as Actual.
• Now create a Second Sales Invoice, TCS will be deducted from the Net Total but the amount will not be rounded off.

Note: Currently it is required only for Sales Invoice(TCS).

backport-version-14
backport-version-15

Frappe Support Issue: https://support.frappe.io/app/hd-ticket/28906

Note: Currently it is required only for Sales Invoice(TCS).

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This is an automatic backport of pull request #45271 done by [Mergify](https://mergify.com).