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	$110.55	11.493%	$123.2555	$123.26	$123.25	$123.30
Purchase #2	$104.88	6.400%	$111.5923	$111.59	$111.60	$111.60
Purchase #3	$47.96	11.241%	$53.3512	$53.35	$53.35	$53.40
Purchase #4	$231.98	4.223%	$241.7765	$241.78	$241.80	$241.80
Purchase #5	$181.90	9.312%	$198.8385	$198.84	$198.85	$198.80
Purchase #6	$20.81	10.650%	$23.0263	$23.03	$23.05	$23.00
Purchase #7	$66.35	6.756%	$70.8326	$70.83	$70.85	$70.80
7 purchase totals =	$764.43		$822.6729	$822.68	$822.75	$822.70