GST core
Rounding
Rounding is how GST amounts are adjusted to whole cents on invoices and, where permitted, to whole dollars on the BAS, so figures reconcile cleanly without mistaken adjustments.
GST calculations often produce amounts with fractions of a cent. Ten per cent of $12.34, for instance, is $1.234. Since you cannot charge or pay a fraction of a cent, the figure has to be rounded. The common approach is to round to the nearest cent, rounding up where the fraction is half a cent or more. Consistency is what matters most, so pick a method and apply it the same way across your invoices.
For business operations, rounding comes up in two places. The first is on individual tax invoices and receipts, where the GST shown is a dollar and cent amount. The second is on the Business Activity Statement, where the labels generally call for whole dollars. The ATO guidance for BAS lets you report in whole dollars, so you do not have to chase cents when entering totals. Check the current ATO instructions for the preferred way to round or omit cents.
Rounding becomes more noticeable when you have a lot of small sales. If a retailer calculates GST on every single item and rounds each one, the total can differ from the GST calculated on the whole basket. Neither is necessarily wrong, but the invoice should show GST consistently. Many point of sale systems calculate GST on the transaction total to avoid accumulating tiny differences.
Price display also involves rounding. Where goods carry a GST-exclusive price, the GST-inclusive price a customer pays is the exclusive price plus the GST, rounded to a cent. Cash transactions have an additional rounding effect, because Australia no longer uses one-cent and two-cent coins. Cash totals may be rounded to the nearest five cents, but this is a payment matter and does not change how the GST amount on the invoice is worked out.
Rounding does not change whether something is taxable. It only affects the precise dollar figures. If you notice that your accounting software shows a one-cent difference compared with a supplier invoice, that is usually a rounding difference and not a sign of an error. If you repeatedly find larger variances, though, you should investigate, because the cause may be a wrong tax code or a mis-keyed amount.
For credits, the rule is that you claim what the tax invoice shows, or what the law calculates, not an amount rounded in your favour. Systematically rounding up credits or rounding down GST payable could be treated as an incorrect claim if the amounts are material. Keeping a clear record of how figures were calculated protects you in a review.
Rounding conventions can also differ between systems, which is why reconciliation matters. This page is general information only, and you should confirm the right approach for your business with the ATO or a registered tax professional.
Worked example
A retailer sells three items, each priced at $12.34 excluding GST. GST on each, worked item by item, is $1.234, which rounds to $1.23, giving $3.69 in total. Calculated on the basket, GST is 10% of $37.02, which is $3.702, rounding to $3.70. The one-cent difference is a rounding effect. On the BAS the retailer reports only whole dollars for the period.
Practical tips
- Choose one rounding method, such as the nearest cent on the invoice total, and apply it consistently every time.
- Do not worry about one-cent differences, but investigate larger or repeated variances because they often indicate a coding mistake.
- Never round credits upwards in your favour. Claim the amount shown on the tax invoice.