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	$42.81	8.828%	$46.5893	$46.59	$46.60	$46.60
Purchase #2	$173.32	7.203%	$185.8042	$185.80	$185.80	$185.80
Purchase #3	$224.45	11.685%	$250.677	$250.68	$250.70	$250.70
Purchase #4	$48.33	7.320%	$51.8678	$51.87	$51.85	$51.90
Purchase #5	$28.50	13.756%	$32.4205	$32.42	$32.40	$32.40
Purchase #6	$63.54	4.640%	$66.4883	$66.49	$66.50	$66.50
Purchase #7	$100.48	10.271%	$110.8003	$110.80	$110.80	$110.80
7 purchase totals =	$681.43		$744.6474	$744.65	$744.65	$744.70