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	$112.76	7.103%	$120.7693	$120.77	$120.75	$120.80
Purchase #2	$47.49	10.663%	$52.5539	$52.55	$52.55	$52.60
Purchase #3	$97.71	13.852%	$111.2448	$111.24	$111.25	$111.20
Purchase #4	$50.94	13.243%	$57.686	$57.69	$57.70	$57.70
Purchase #5	$242.54	3.168%	$250.2237	$250.22	$250.20	$250.20
Purchase #6	$229.62	11.466%	$255.9482	$255.95	$255.95	$255.90
Purchase #7	$139.31	9.136%	$152.0374	$152.04	$152.05	$152.00
7 purchase totals =	$920.37		$1,000.4633	$1,000.46	$1,000.45	$1,000.40