Hello,
You are right on both points, and both are done in version 5.1.0 of the PDF invoice plugin, which you can download now.
The rounding first. BT-114 is indeed the mechanism for it. The VAT of the breakdown has to be the taxable base times the rate, 28.06 x 7% = 1.96, while HikaShop rounds the tax of the product and of the shipping separately, 1.64 + 0.33 = 1.97, so the two are a cent apart. The grand total stays the sum of the base and the tax, which BR-CO-15 requires, and the cent goes in the rounding amount, so that what is due is the total of the order:
<ram:TaxBasisTotalAmount>28.06</ram:TaxBasisTotalAmount>
<ram:TaxTotalAmount currencyID="EUR">1.96</ram:TaxTotalAmount>
<ram:RoundingAmount>0.01</ram:RoundingAmount>
<ram:GrandTotalAmount>30.02</ram:GrandTotalAmount>
<ram:TotalPrepaidAmount>0.00</ram:TotalPrepaidAmount>
<ram:DuePayableAmount>30.03</ram:DuePayableAmount>
The amount due follows BR-CO-16 in both cases, whether the invoice is written as paid or not, and the rounding element is only there when the breakdown and the order total differ. The UBL file of an invoice or a credit note does the same with cbc:PayableRoundingAmount.
This does not depend on your "Round prices during calculations" setting: the document is compared with the total of the order however that total was reached, so the file settles on what the customer has to pay in both modes. The amounts of the Factur-X and UBL files now also follow the decimals the currency of the order is written with, as HikaShop and the payment plugins do, and what the file may carry as a rounding follows the same step, with at least the rounding increment of a currency that has one, like the five centimes of the Swiss franc. A larger difference is left alone rather than called a rounding.
One more thing of the same version, since your bank transfer orders are invoiced before the money arrives: the new "Say how to pay the invoice" setting makes those invoices say how. Fill in your IBAN, the account name and the reference you want quoted, and the Factur-X and UBL files carry the payment means next to the amount due, so the customer's accounting knows where the transfer has to go. What kind of instruction it is follows the payment method of the order, a transfer for yours and a cheque for an order paid by cheque.
The font path is ours, and 5.1.0 takes the plugin out of the way. It does not define K_PATH_FONTS at all any more: the document now names the definition file of each face it draws with, read from its own folder, so it needs no shared constant to find its fonts. HikaSerial then defines that constant itself, with the trailing slash its TCPDF expects, as it does on a site where our plugin is not installed. After the update you should be able to put back the original _getfontpath() of HikaSerial and remove the Helvetica files you copied into the tc-lib-pdf-font folder. Jerome is also planning on updating TCPDF in HikaSerial and moving it into a namespace of its own, which will settle the double load itself.