Joe I am sure that the increments are constant, and set at the start of each individual records auction. The variable is each bidders maximum bid.
Confusing as I said earlier as it is a pure fluke if the finishing price can be divided by the increment.
As soon as a bidder puts a maximum bid, that beats a previous maximum bid, it will jump to that then add the increment.
Have you tried working out the increments on Ebay
Martyn