Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.81	8.624%	$43.2432	$43.24	$43.25	$43.20
Purchase #2	$162.55	8.786%	$176.8316	$176.83	$176.85	$176.80
Purchase #3	$16.91	7.517%	$18.1811	$18.18	$18.20	$18.20
Purchase #4	$40.56	7.795%	$43.7217	$43.72	$43.70	$43.70
Purchase #5	$48.42	8.125%	$52.3541	$52.35	$52.35	$52.40
Purchase #6	$37.26	11.444%	$41.524	$41.52	$41.50	$41.50
Purchase #7	$151.89	3.249%	$156.8249	$156.82	$156.80	$156.80
7 purchase totals =	$497.40		$532.6806	$532.66	$532.65	$532.60