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	$230.55	12.320%	$258.9538	$258.95	$258.95	$259.00
Purchase #2	$105.25	4.214%	$109.6852	$109.69	$109.70	$109.70
Purchase #3	$245.33	7.374%	$263.4206	$263.42	$263.40	$263.40
Purchase #4	$164.28	4.733%	$172.0554	$172.06	$172.05	$172.10
Purchase #5	$37.33	6.716%	$39.8371	$39.84	$39.85	$39.80
Purchase #6	$58.84	10.845%	$65.2212	$65.22	$65.20	$65.20
Purchase #7	$47.82	12.307%	$53.7052	$53.71	$53.70	$53.70
7 purchase totals =	$889.40		$962.8785	$962.89	$962.85	$962.90