Yes the payout varies accordingly to the internal price of Steem, known as Feed Price, which is a 3.5 days moving average of market Steem Price.

Scenario, let's do away with curation and beneficial rewards, and assume your post has a $1 pending author payout. Assuming today is the 7th day and the Feed Price is exactly $1. You will receive 1 Steem as payout.

Same scenario, but this time the Feed Price is $2. Now you will receive 1/2 = 0.5 Steem. Actually, you receive 0.25 Steem and 0.25 Steem power. Things get a little complicated when the blockchain starts printing SBD. Let me know if you need information on that.

Another thing to note, the pending payout is also dependant on the Feed Price.

Scenario, assuming you had just created a post and it has a pending author payout of $1, and the Feed price is $1. But at the 7th day, the Feed Price increased to $3. Your pending author payout will follow and increase too (the $ value that you see on your steemit post). There is a complex algorithm behind this, your pending payout could be somewhere along $2 or more. For more information, you can read up on this post. https://steemit.com/steemit/@jbn/steemit-guide-how-vote-value-is-calculated-on-steemit-and-factors-affecting-vote-value