Start with a confirmed amount and an uncertain category
Use what the statement can really show: date, merchant and final transaction amount. It may not tell you which items were in the basket or who used them. Keep “paid” separate from “share agreed.” That prevents a known total from giving a guessed split the appearance of precision.
Reconstruct only the detail needed
For the $24 hardware purchase, ask whether the shower rail was the only item or if the shopper also picked up a personal brush. If both people remember the brush was $6, the remaining shared portion is $18. If neither remembers the price, note the uncertainty rather than inventing a price to balance the record.
Close the entry with the right confidence
Ask the shopper one narrow question, such as whether the paintbrush was on that receipt. If a return or reimbursement depends on exact items, ask the shop about a copy. Until then, keep any estimated split visible as an estimate.
A household may decide to split this one ambiguous charge equally to finish the week's review. Label that as an agreement, not a reconstruction of the receipt. If a receipt later appears and the difference matters, both people can see what assumption to revisit.