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	$40.63	4.743%	$42.5571	$42.56	$42.55	$42.60
Purchase #2	$184.83	11.176%	$205.4866	$205.49	$205.50	$205.50
Purchase #3	$95.83	3.156%	$98.8544	$98.85	$98.85	$98.90
Purchase #4	$59.94	3.592%	$62.093	$62.09	$62.10	$62.10
Purchase #5	$103.76	13.772%	$118.0498	$118.05	$118.05	$118.00
Purchase #6	$40.70	8.478%	$44.1505	$44.15	$44.15	$44.20
Purchase #7	$48.65	6.211%	$51.6717	$51.67	$51.65	$51.70
7 purchase totals =	$574.34		$622.8631	$622.86	$622.85	$623.00