Hi, I used to work for U.S. Cusoms. You don't pay "taxes" to Customs, you pay "taxes" to the IRS. You do pay "duties/duty" to Customs, when applicable. Some items are "duty free" always, or can be "duty free" dependeing on the country of origin, that is where they were made, not where they were purchased from. Duty rates on basses appera to be as follws:
(this is from the book CBP uses to classify merchandise & assess rates of duty

Harmonized Tariff Schedule of the United States (2009) (Rev. 1)
Annotated for Statistical Reporting Purposes
Other string musical instruments (for example, guitars,
violins, harps):
9202.90 Other:
Guitars:
9202.90.20 00 Valued not over $100 each, excluding the value
of the case ............................. No. ..... 4.5%
Free (A,AU,BH,CA,CL,E,IL,J,JO,MA,MX,OM,P,PE,SG)
9202.90.40 00 Other (valued over $100 each).................................. No. ..... 8.7%
Free (A,AU,BH,CA,CL,E,IL,J,JO,MA,MX,OM,P,PE,SG)
9202.90.60 00 Other (other than a guitar)..................................... No. ..... 4.6%
Free (A,AU,BH,CA,CL,E,IL,J,JO,MA,MX,OM,P,PE,SG)
The number "9202.90.20, for example, is the classification number for a guitar.
Where it says "free" followed by letters such as "CA,MX,SG, etc," these stand for the names of countries whose particular products (in this case, guitars) are "duty free." The letters may also stand for particular trade agreements, which again may reduce the rate of duty. You may have to pay "merchandise processing fees," insurance, Customs brokers fees, etc, on top of duty. Best to call your local CBP office before you buy something from outside the U.S. As they say, "know before you go." Hope this helps!