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	$85.78	5.439%	$90.4456	$90.45	$90.45	$90.40
Purchase #2	$139.42	10.111%	$153.5168	$153.52	$153.50	$153.50
Purchase #3	$16.85	13.451%	$19.1165	$19.12	$19.10	$19.10
Purchase #4	$250.68	3.226%	$258.7669	$258.77	$258.75	$258.80
Purchase #5	$133.55	6.122%	$141.7259	$141.73	$141.75	$141.70
Purchase #6	$127.43	12.394%	$143.2237	$143.22	$143.20	$143.20
Purchase #7	$236.48	13.615%	$268.6768	$268.68	$268.70	$268.70
7 purchase totals =	$990.19		$1,075.4722	$1,075.49	$1,075.45	$1,075.40