In Accounting Settings there is now Cash Roundings which should provide the feature. For odoo versions which do not have that feature there are apps under the topic swedish rounding.

First you have to enable Cash Rounding in Accounting Settings

After you need to configure Cash Rounding like that *use better Profit and Loss Accounts :-)

In the Invoice you can then use it in Other Section as Cash Rounding Method

If it is selected it will round the value with some extra line

like configured in the Cash Rounding.

There is also the otption to use "modify tax amount".

The answers are treating rounding for Invoices and PoS, that are configurable in Odoo. However, for Sales and Purchases there are not configurations.

A way that works for both (SO and PO), but is a change that also affects taxes and may be not accepted by all accountants, would be to change the currency rounding factor:

or a solution that works only for sales product prices, would be through Pricelists rounding factor: