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	$222.68	3.800%	$231.1418	$231.14	$231.15	$231.10
Purchase #2	$130.69	6.506%	$139.1927	$139.19	$139.20	$139.20
Purchase #3	$110.86	9.663%	$121.5724	$121.57	$121.55	$121.60
Purchase #4	$205.62	8.404%	$222.9003	$222.90	$222.90	$222.90
Purchase #5	$106.32	5.257%	$111.9092	$111.91	$111.90	$111.90
Purchase #6	$107.64	3.143%	$111.0231	$111.02	$111.00	$111.00
Purchase #7	$16.74	13.828%	$19.0548	$19.05	$19.05	$19.10
7 purchase totals =	$900.55		$956.7943	$956.78	$956.75	$956.80