This has been going on for a long time. Almost ten years ago when I was coming to USA, my travel agent advised me to keep about 5 to 6 thousand Nepalese ruppes in my pocket. He told me that the immigration officers in airport give troubles and advised me to hand them couple of thousand of rupees if such situation occurs. Therefore I carried about ten thousand Nrs with me while coming to USA. Fortunately the officer let me go without any problem. I have not returned Nepal since then. I still have those 10000 NRS rupees with me.