@MMAF 

No, it does not impact your sale from Jan. 5.  In your example, the COGS is $100 for the Jan. 5 sale and your COGS will be $150 on your next sale.  QBO uses the first-in, first-out (FIFO) inventory method.  So, the item purchased first gets booked to COGS, then the subsequently purchased item, etc, etc.