You goal should be in rupees, as you are earning in rupees and spending in rupees. Any other currency is of no value / meaning.
More than being worried about the USD/INR rate, you should be worried about inflation and savings rate. This will change the amount that you need to save for your retirement. The USD/INR rate would anyways get reflected into some of the prices of some of the items and would get relfected into Inflation.
Your savings goal should not be an arbitrary number. It should have a purpose. The purpose for saving goal could be to meet education in future, wedding, kids education, vacation, downpayment for house, retirement etc.
Say your goal is to save enough for you Masters degree that you plan to do after 3 years.
Say As of today you find the cost fees/book/etc is Rs 100,000 for you Masters degree. Say Additional Rs 100,000 for your stay & food expenses.
So essentially you need to save Rs 200,000 in next 3 years. However here is the catch, in 3 years time the inflation around 10% may mean you need to save Rs 200,000 * 1.1 = 220,000 at the end of first year, and 220,000 * 1.1 = 242000 for second year, and 242,000 * 1.1 = 266,200. So essentially you need to save more. If you run this in XLS it will be easy to track and moniter. Now at the end of 1st year whatever you have saved, you may keep it in short term fixed deposits, this would get you interest. So effectively this calculation will tell you how much you need to save monthly.
For longer goals, you may say decide to invest the money in shares / PPF / or other instruments, the essential is same the returns that you are getting adds value and the inflation removes value.