# Penny Rounding

What a cash total actually rounds to now that the penny is gone.

**Why delegate it:** Four things are wrong in most explanations and each changes the answer: rounding is cash-only, applies to the total rather than each item, happens after tax, and is not free money for retailers. Money in floating point is also a bug waiting to happen.

Site: https://penny-rounding.gumballtools.com

## Tools

### `round_cash_total` — Round a cash total the way the post-penny rules work

Settle a transaction: exact subtotal, tax computed on that exact subtotal, then round the final total to the nearest nickel — and ONLY for cash. Card, EFT and gift-card payments stay priced to the cent, so the same basket legitimately comes to two amounts. Rounding applies to the TOTAL, never per item. A final digit of 1, 2, 6 or 7 rounds down; 3, 4, 8 or 9 rounds up. A string amount is read as dollars, a number as integer cents. Not legal or tax advice — there was no federal rounding law as of September 2026 and state law varies.

Direct endpoint: `https://penny-rounding.gumballtools.com/api/v1/settle`

### `rounding_impact` — What cash rounding is actually worth

Compute the mean rounding delta per cash transaction across a price list. Answers "does rounding make retailers money" with arithmetic rather than a guess: symmetric rounding nets to essentially zero by construction. Pass always-up to quantify the "just round everything up" idea, which is worth about 2 cents a sale and which no jurisdiction has adopted for retail.

Direct endpoint: `https://penny-rounding.gumballtools.com/api/v1/impact`

### `price_band` — Find every list price that settles to the same cash total

For a list price and a tax rate, finds every nearby list price that settles to the SAME cash total, and the highest one. Use it for "what should I charge" and "can I price to gain from rounding" questions.

There is exactly one free move here and it is easy to get backwards, which is why this is worth a call rather than a calculation. Rounding collapses a band of five consecutive list prices onto one nickel: at 0% tax, $19.98 through $20.02 all settle to $20.00 in cash. Within that band the cash collected is identical, so the highest price in it is strictly better — the same from cash customers and up to 4 cents more from every card customer.

The move that looks clever and is not: pricing BELOW a nickel so rounding "adds" a couple of cents. You collect the same cash and less on card. The rounding delta is not revenue, and this tool will not recommend it.

Returns the whole band, the highest price in it, and the free gain in cents — never more than 4.

Direct endpoint: `https://penny-rounding.gumballtools.com/api/v1/price-band`

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Via the aggregator: `https://gumballtools.com/api/mcp`
Direct: `https://penny-rounding.gumballtools.com/api/mcp`