Currently, it is only possible to define in general in the "Purchases & Payables Setup" whether an invoice rounding should be performed or not.
Suppliers are very different regarding invoice rounding, i.e. some vendors round their invoices and others do not. For this reason, it should be possible to specify per vendor whether invoice rounding should be performed or not.
It would be best to implement this in a similar way as for the items with regard to the "Prevent Negative Inventory" field. With the option "Default" the setting according to "Inventory Setup" applies and with the option Yes or No the setting according to the respective item applies.
Especially in Switzerland, many BC customers struggle with this problem, as about 70% of the vendors round their invoices to 0.05 and the rest do not. This means a lot of manual and complicated handwork so that the purchase invoices can be created and posted correctly.