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	$61.40	6.146%	$65.1736	$65.17	$65.15	$65.20
Purchase #2	$63.55	10.492%	$70.2177	$70.22	$70.20	$70.20
Purchase #3	$53.63	8.607%	$58.2459	$58.25	$58.25	$58.20
Purchase #4	$54.99	7.399%	$59.0587	$59.06	$59.05	$59.10
Purchase #5	$105.89	4.854%	$111.0299	$111.03	$111.05	$111.00
Purchase #6	$27.45	7.189%	$29.4234	$29.42	$29.40	$29.40
Purchase #7	$107.83	9.508%	$118.0825	$118.08	$118.10	$118.10
7 purchase totals =	$474.74		$511.2317	$511.23	$511.20	$511.20