How can i prevent buyers giving me a poor star rating on postage cost when i charge $6 for a $6.60 postage item!?

[kenny-gee999]

I post all my items below postage cost and it clearly shows it on the post bags. I post the next day so buyers recieve very quickly. I would love to charge less postage on items but then, like all sellers experience, i start to loose money instead of make money! So i dont understand why my postage cost star rating is so low!! Any ideas??