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	$122.28	4.724%	$128.0565	$128.06	$128.05	$128.10
Purchase #2	$153.33	8.163%	$165.8463	$165.85	$165.85	$165.80
Purchase #3	$54.25	10.512%	$59.9528	$59.95	$59.95	$60.00
Purchase #4	$153.56	5.767%	$162.4158	$162.42	$162.40	$162.40
Purchase #5	$118.95	7.500%	$127.8713	$127.87	$127.85	$127.90
Purchase #6	$55.91	6.368%	$59.4703	$59.47	$59.45	$59.50
Purchase #7	$151.40	11.767%	$169.2152	$169.22	$169.20	$169.20
7 purchase totals =	$809.68		$872.8282	$872.84	$872.75	$872.90