Choosing the right tube for my tire I wanted to change my bike tire. Is it okay to use 26x1.90 inner tube with 26x1.95 tire?
Inner tubes work over a range of tire sizes.  The difference between 1.9 and 1.95 width is insignificant for the tube.  Go ahead and reuse it.  You can look in the shop at what range the tubes claim to cover.  My quick look at one online store showed two tubes rated for 26x1.5-2.0, which cover your range, and one rated 26x1.95-2.25.  In theory you shouldn't have the last one, but I am sure it would work for 1.9 just fine.