You will pay 16% sales tax on anything you order over the internet; if your purchase originates from within Germany you also pay it but it's included in the price. This tax applies to the postage or shipping charges as well. You can be expected to pay a German Customs fee (Zollgebühr) ranging from 3 - 16% on books, CDs, DVDs, clothes, etc. On one recent clothes order (From L.L.Bean - BH) the customs fees were a horrifying 33 %! The postman will expect cash on delivery so be prepared. You have to pay the custom duties even if family or friends in the U.S. send items to you as gifts. The computation of these additional customs fees seems to be somewhat random - some high value items come through without extra fees and duties, whereas other small ticket items (i.e., 50 worth of clothing from L.L.Bean) come with a demand for customs (i.e., the afore-mentioned horrifying 16).
Postal costs when shipping from the U.S. to Germany are far cheaper than shipping goods to the U.S. from Germany. When shipping from Germany, small packages (Päckchen) weighing under 2 kilo can go by a very cheap rate (approx. 8) and take up to 4-6 weeks to reach the western zone in the U.S. For approx. 20, your package can go much more quickly by Airmail. Larger packages (Postpaket) weighing over 2 kilo do not qualify for the cheaper, slower method of travel and will always be more expensive and quicker to arrive at their destination. Ask for a booklet called Service-Informationen at the Post Office that will outline all the options available - plan light and in advance to save the most!