What should be my sampling frequency?
Much depends on what you want to deduce from your data.

In general,  if your sample rate is not uniform, your measurements should be accurately time stamped.

The nearer to an average of 1/10 a second your sample intervals are the better. 

A typical hueristic used in Engineering is the 1/10 rule, so if your samples are within 1/100 of a second of 1/10 second sampling, you probably can just assume they are uniformly sampled, but again, it really depends on what your measurement's purpose is.

Again if you have timestamps, there are methods to interpolate your measurements to uniform time increments. There is the timeseries class in Matlab which has a method for this purpose, which is an example of how to treat nonuniform samples.

If you don't have the ability to accurately time stamp data, you could use the average of sample intervals.  Like all practical solutions to problems you need to use your own judgement to determine if what you do is adequate. 

We really can't make that judgement for you.