Repairs/Maintenance or small tools & supplies?

I'm never sure how to categorize some purchases.  Obviously, if my guys purchase a shovel, a new chain for chainsaw, or blades for the PVC cutter (basically any expendible tool/supply), these are considered Small Tools & Supplies.  Likewise, if we take a truck or skidsteer in for servicing, it's Repairs and Maintenance.  But if we purchase motor oil, brake fluid, a truck battery, or DEF (diesel exhaust fluid), would that be considered a purchase for R&M or SmT&S?  My accountant says it really doesn't matter, as they are all expenses, but I ponder this questions weekly when I code transactions and really want a fixed answer to stick with...