For us in the UK 2 weeks ago, TNT (the courier) use a conversion rate of 1 : 0.9923 (Euro : GBP). TNT (via CAP Gemini) charged Β£15.30 processing fee.
so multiply your product charge total by 0.9923
then mutiply the result by 20%
then add Β£15.30
To note, CAP Gemini are used as an outsource for tax collection, hence the conversion rates are VERY high. They took about a week to contact us once the package had landed at the TNT hub.