Underline entire row based on first cell

Good afternoon

I am looking to underline a row based on the line item of an order in the first column, so that we can easily see the orders grouped together. Each order may have a different amount of products, and lines can be added or removed. I assume maybe formatting column A to look at the cell above and underlining when it changes, but I wasn't sure how to make that translate the entire length.

Thanks
Brent