The VAT and US Customs Tax are two different/unrelated issues.
In Europe, unlike in the US, their tax (VAT of approx. 20%) is added to the price of the merchandise as shown on the tags rather than added at checkout. The VAT also refundable to non-EU residents departing the EU with their purchases; however, the actual refund amount is only around 12-13% after fees and there are very specific requirements. You will find lot of useful information on the VAT Refund process, requirements, tips, etc. in this thread. The VAT Refund process is handled before you leave the EU.
US Customs Tax is handled as you re-enter the US with the merchandise and go through customs. The first $800 for individuals/$1600 for couples is exempt from US Customs Tax. The next $1,000 is subject to a flat 3% Customs Tax. Any amounts over that are taxed based on the Harmonized Tariff Schedule (which I believe is currently 6.5% for handbags). So if you are traveling alone/not as a family you would pay the following taxes on $5,000 worth of handbags (Note: The amount you declare should be the amount after the VAT Refund and you should have receipts and copies/photos of VAT Refund Forms available as evidence):
First $800 = Exempt/No Tax
Next $1,000 = $30
Remaining $3,200 = $208
Total US Customs Tax Due = $238
Many of us have had experiences with customs agents waving us through without charging US Customs Tax or being charged less than than the actual tax due, but other times we've been charged the full US Customs Tax. It seems to vary depending on the agent, but even if you are charged the full US Customs Tax, there is still a significant savings. Enjoy your trip and have fund shopping!