Keep money in whole pence
The merchandise amount becomes exactly zero when a confirmed merchandise-only credit equals the subtotal. Our three dated package prices total 990 pence,or £9.90. A £9.90 credit therefore leaves £0.00 merchandise. A £9.91 credit exceeds that subtotal and is rejected; the tool does not produce a negative purchase amount or pretend an unsupported voucher pays you.
Allow exact merchandise zero
Money is parsed from nonnegative GBP strings with at most two decimal places and stored as integer pence. Whole package quantities are multiplied before display rounding. This avoids a binary-decimal comparison rejecting a legitimate full credit. For example,two user-entered £47.99 packages total £95.98 exactly,and three £0.10 packages total £0.30.
Retain delivery and other charges
A merchandise credit does not automatically erase shipping,collection or other separate charges. With merchandise at zero,a confirmed £4.99 delivery and £1.25 other actual charge would still total £6.24 if all other entered charges are explicitly zero. These are arithmetic test inputs,not observed shipping fees or a promise that a retailer accepts such a credit.
Reject missing or invalid inputs
Leave unknown charges blank and the full total stays unresolved. Negative values,exponent notation,more than two money decimals and amounts above the stated limit are rejected. Keep already-included VAT separate from genuinely additional charges to avoid double counting. The ledger makes no checkout submission,voucher validation or cross-retailer shipping assumption.
Sources & scope
Checked November 5, 2026. Manufacturer and retailer references support the specific statements. Dated displayed prices are not final checkout quotes, performance rankings or performance testing. This shopping reference does not replace the exact product label or retailer instructions. Current received labels and independent household-paper/content/commerce review remain pending.
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