Grouping some data in a bar chart

[graph1981]

This is a relatively simple chart question. I have some cost data for 5 different technologies that I would like to plot in a graph. the technologies belong to 3 unique categories and I want to group them on the chart so that there is no gap between technologies in a same category.
I have a graph where they are grouped by title of the category but would anyone know how I may remove the gaps between the individual bars in the same category?
Thank you!