Yes, you need to be cautious when placing your bid for each individual keyword.
With each keyword you are given a suggested bid, it is important to be close to that bid whether you choose to go lower or higher than it.
It is also recommended that you look at the monthly searches and competition of that keyword. This can help you determine what bid to place on the keyword. You may want to bid higher or lower depending on these analytics.
In sequential rounds you will be able to see a more specific low-high amount per keyword that was used previously. This is done by clicking on the blue pencil next to the keyword on the Pay per Click page. A small window will then appear. If your bid is too high or too low, it will also be highlighted.