Ahab is right.
If you read the way ebay works it only bids in increments that are specified.
That is if the increment is $5 say.
The item current high bid is $25.
You could bid $100 but it would only bump the bid to $30 providing there are no other pending bids with limits.
The easiest way to learn how it works is to watch a few items that you know will have activity.
Hope this helps.
JLK