If you have a place to dispose of them then fine but otherwise don't worry. It's only official waste that must be disposed of properly by law. What you can do though is to take a strong container, seal it and make a small hole in the top or an X cutout. After it's full you can tape it up properly and make sure it's unidentifiable and inconspicuous so people won't be messing around with it. After this it's usually safe to just throw in the thrash until some day when our descendants have to incinerate all our trash anyway, or at least safer than all the people just throwing their open needles in the trash. If you take it somewhere for proper disposal though you can just skip the last step. It usually takes years to fill up so won't be much of a problem either way.