Prepare a Fix for a Reviewed Bug and Document the Verification Plan

Problem/Feature Description

A reviewer on PR #289 (fix/order-totals-rounding) caught a real bug: the calculateOrderTotal function silently truncates sub-cent values instead of rounding them, leading to off-by-one errors on orders with multiple discounts. The review comment includes a reproducing example. The PR also changes the /api/v1/orders/total endpoint response shape slightly — a field was renamed from raw_total to rawTotal to match the camelCase convention used everywhere else.

You need to plan and document exactly how you would address this feedback and bring the PR to a state ready to push. Produce a written plan rather than actually running the commands.

Output Specification

Produce a file called fix_plan.md that describes, in order:

1. Bug reproduction: how you would confirm the bug exists before making changes, and what you would verify
2. Code change: what you would actually change in the production code (one or two sentences — keep it surgical)
3. Verification commands: the exact shell commands you would run locally before pushing, given that both application logic AND an API shape changed
4. Commit message: the exact commit message you would use, formatted correctly for automated changelog tooling
5. What you would NOT do: any tempting shortcuts you are explicitly ruling out and why