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	$146.62	5.593%	$154.8205	$154.82	$154.80	$154.80
Purchase #2	$104.79	6.314%	$111.4064	$111.41	$111.40	$111.40
Purchase #3	$127.57	3.325%	$131.8117	$131.81	$131.80	$131.80
Purchase #4	$59.74	9.790%	$65.5885	$65.59	$65.60	$65.60
Purchase #5	$80.51	10.617%	$89.0577	$89.06	$89.05	$89.10
Purchase #6	$241.61	13.829%	$275.0222	$275.02	$275.00	$275.00
Purchase #7	$27.62	3.123%	$28.4826	$28.48	$28.50	$28.50
7 purchase totals =	$788.46		$856.1896	$856.19	$856.15	$856.20