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	$178.27	12.420%	$200.4111	$200.41	$200.40	$200.40
Purchase #2	$52.84	9.453%	$57.835	$57.84	$57.85	$57.80
Purchase #3	$247.62	7.870%	$267.1077	$267.11	$267.10	$267.10
Purchase #4	$80.41	12.628%	$90.5642	$90.56	$90.55	$90.60
Purchase #5	$240.38	5.243%	$252.9831	$252.98	$253.00	$253.00
Purchase #6	$42.85	13.215%	$48.5126	$48.51	$48.50	$48.50
Purchase #7	$148.28	6.634%	$158.1169	$158.12	$158.10	$158.10
7 purchase totals =	$990.65		$1,075.5306	$1,075.53	$1,075.50	$1,075.50