Managing Opening and Closing Balances in Accounting SW

Question

Hi
I am developing an accounting software. It contain the most important part of giving ledger of customer or ask for ledger from supplier or check the stock at any time of FY year.
When i do this i have to show opening balance of customer.  ( if the ledger is from suppose 1st June till 31st July) then i will have to show the opening balance on 1st of June of that customer and from there on i will have to show the sales he made on left and payment made of right and finally at the bottom, its calculation with current balance. How i should calculate the opening balance on 1st June. This is making me crazy. As the same things i will have to adopt in different places like showing current stock, showing stock at particular month.

So please give me some advices how should i maintain the balance or calculate the balance, do i have to make a table and save the everday balances or any other thing, kindly please give some tables structure along with some description.
Thanking millions in advance