@ellswortha
Yes, if using periodic inventory you should be posting all inventory purchases to a temporary 'Purchases' asset clearing account. You should not post directly to COGS. If you post directly to COGS, your interim financial statements will be inaccurate because your COGS is reflecting the amount of inventory purchased, not the amount of inventory sold. When you take a physical inventory at year-end and make the adjusting journal entry, you will be accurate for the year only, but not any interim dates.
The proper way to use periodic inventory is to post all purchases to a 'Purchases' asset account or multiple purchases accounts, depending on the level of detail you desire. At month-end (or however frequently), you will make the following entry:
Debit ending inventory amount (if estimate, you will back into COGS, see below)
Debit COGS (if estimate, you will back into ending inventory, see below)
Debit Purchase-Discounts (if you track it)
Credit Freight-In (if you track it separately)
Credit Purchases (to clear)
Credit beginning inventory
You will need to estimate either COGS (gross profit method) or ending inventory (retail inventory method) based on which you feel is more accurate. That is the limitation of using periodic inventory. I have a company that uses periodic inventory and has for almost 20 years so COGS is the better estimate and then we back into ending inventory. If you have a way of getting a more accurate ending inventory than gross margin, go that route and back into COGS.
