According to the law..
the tax is exempted in case of nepali citizen returning from foreign country in following case...
One piece each of professional goods used by the
professional passenger( for example for medical doctor
stethoscope and instruments for testing blood pressure, for
players goods like football, volleyball, badminton set,
musician
harmonium, tabla etc);
for
ordinary
musical
instruments
like
guitar,
here are other information..
https://docs.google.com/viewer?a=v&q=cache:eI4BAN8dedUJ:www.customs.gov.np/download.php%3F%26f%3DBaggage%2520Rules%25202066%2520Final.pdf%26dir%3Dcontents+&hl=en&gl=us&pid=bl&srcid=ADGEESjRroikNt-zmqoSP6CFsLL8EL7UO9o2nI_bMcYuQar_sfKaJ6GU3atJjR5Uu1zIkZfB7UvIujzB7sZV54MJH7f-iKYrPv4UJ75thpVZqiYbDMeRKFOOpakcNQO6nbkZ6w1gQJqS&sig=AHIEtbSDGDo1ZgvnVD7jN4NyVYeztlu4vQ