How to solve purchase price & sell price change?

I have problem that price changes at middle of the accounting period for examples Year 2014/1/1 price of the ABC product was Rs.105 But at 2014/5/20 price increase to 115 As same way selling price was 110 but at 2014 /5/20 selling price increase to 125. In this case how can I solve this problem?

When creating invoice or payment, simply record the price you’ve actually purchased the item for.

If you are asking about those fields which ask you to enter Sale price when creating item in Manager, those just fields for auto-complete purposes when creating new invoice so you don’t have to keep entering price manually over and over again.