Jeimer making $5M (plus incentives, but I'll ignore them for this point) versus $7M. Let's say the trade is now, at the mid-season point to make the math easy. A team picking up $5M Jeimer adds roughly $2.5M to their CBT bill. A team picking up $7M Jeimer adds roughly $3.5M to their CBT bill.
Let's say that the team acquiring has $3M left under the cap... a bit too precise for practicality based on the approximations on the margins with benefits and back-end roster machinations... but bear with me. The team picking up $3.5M Jeimer would go over the tax. Yes, the tax is only 20% of $500,000 (assuming they are a first time payer), or $100,000: chump change.
But... if they are trying to reset their tax liability, that could set them back. If they want to sign a QO free agent this upcoming offseason, it will cost extra draft picks. If they are losing a free agent this offseason, they will get a 4th rounder instead of a 1st or 2nd rounder in compensation. If they sign a QO free agent, they are also set to lose $1M instead of $500K from their international bonus pool. Remember a lot of those deals are agreed to ahead of time, so the extra money lost their could wreck their entire international signing class.
That immediately prior paragraph is why teams want to stay under. It's not just money. And that is why every little bit of salary could potentially matter in deadline deals.