Without a doubt that you have had no problem to obtain positions in various careers and was at the short end of things that would be out of your control because of politics in the organization.
With any job application/resume,being honest is key as letting the employer know that you were let go from previous positions and now looking to find new employment. Hiding what has happen to you in your previous job can come back and haunt you when the future employer may conduct a background check and discover why you were let go.
As to answer the question on why you left the previous jobs:
1. Call Center job can be explained that you worked there for a short time frame and was not a fit after the 3 month time frame.
2. Cashier job can be explained the same way as there was a decision on staffing and you were let go because of not being able to keep everyone on staff.
Let the employer know that you've gained wisdom about yourself and your abilities from the experiences and that you have grown and expanded your skills and want to demonstrate that in your new job.
No other way around this but being honest as letting your potential employer know that you wish to do anything required in order to get the job as working from the bottom up. See about having good references in order to counter the dismissed jobs that you had in the past. Good references can be helpful in getting your experiences and skills mentioned to HR in this new company,