You should be able to Round your values in a Query and then base your Chart off of that Query.
Make sure you have selected the calculated field (with your rounded value) for the Values (Y axis) of your Chart.

The screenshot below shows 2 Charts.
The first Chart shows the raw values direct from the table.
The second Chart shows the rounded values from the Query.

If you still can't get the correct results we will need to see some screenshots of how you have set up your Chart.

Hi Kevin,

thanks a lot. It worked. Do you by any chance also have an idea how to show the numbers vertically instead of horizontally?

As far as I'm aware there is no way to change the orientation of a data label in Access Charts. If there is I can't figure out how to do it. I can't see anything in the Chart Settings or the Property Sheet to change it.

Perhaps Richard or Alex can chime in on this one.

I feared as much. Thanks for your quick answers.

No... Unfortunately, the modern charts still have much work to be done by the Access team. That's one of the reasons why I haven't spent a lot of time focused on them in my videos, because they are still woefully underdeveloped. I wish that they would give some love to charts and Access, like they did with Excel. In fact, right now, if I want a good chart with cool options, I just export the data to Excel. The classic charts in Access are just fine for simple things like if you want to see sales over time or profit/loss, but anything complicated, do it in Excel for now.

To format your numbers directly in the Mondern chart I use the Primary and Secondary Values Axis Format properties
For percent, this works well l "#%"
For Rounded numbers, this value also works well  "#,##0"

I have always exported to Excel because I could never get a secondary Axis with Classic charts. Now I can create a secondary axis with Modern charts that gets me close enough to stop using Excell now.
And yes, very limited in formatting the layout of a Modern Chart

Thanks, Brian, this will help a lot