I am trying to post the costs for a container but the accruals are wrong, they are all rounded for some reason

Take a look in the Tools, System Table, Currency. The currency table had both USD and CAD set to only allow up to 2 decimal places. On documents, that is fine, but this setting is for within VISCO, to know when the system should round. You need to go to the System Table, Currency and change the decimal places back to 4, then recalculate the accruals for the PO