^ I think so, yes. But IIRC, I don't think you can club them, if that's your intention. They will be applicable only per additional title you buy in Jan...
Edit - Found the official position on the discounts via reddit. Have a look.
Q: Do purchases under $5 receive credit?
A: Yes, any and all purchases in the digital game store before Dec. 31st will receive credit, regardless of price.
Q: How do I know how many credits I have?
A: Before Jan 3rd, keep count of your purchases, or look at purchase emails to find a total to expect. After Jan 3, you'll receive an email with all of your credits at once, it will tell you how many credits you have. You'll still need to keep count as you spend them.
Q: Can I redeem multiple credits on a single game?
A: No you will only be able to use one credit per purchase during the January Sale.
Q: Can I use a credit on a game that costs $5 or less? (Get the game for free?)
A: Yes, the credit will work on items that cost $5 or less, making them free.