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	$136.65	13.632%	$155.2781	$155.28	$155.30	$155.30
Purchase #2	$235.52	13.586%	$267.5177	$267.52	$267.50	$267.50
Purchase #3	$174.64	11.189%	$194.1805	$194.18	$194.20	$194.20
Purchase #4	$39.50	8.791%	$42.9724	$42.97	$42.95	$43.00
Purchase #5	$175.72	10.314%	$193.8438	$193.84	$193.85	$193.80
Purchase #6	$176.60	13.529%	$200.4922	$200.49	$200.50	$200.50
Purchase #7	$40.73	13.308%	$46.1503	$46.15	$46.15	$46.20
7 purchase totals =	$979.36		$1,100.4350	$1,100.43	$1,100.45	$1,100.50