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	$15.47	11.390%	$17.232	$17.23	$17.25	$17.20
Purchase #2	$48.85	4.189%	$50.8963	$50.90	$50.90	$50.90
Purchase #3	$99.72	10.446%	$110.1368	$110.14	$110.15	$110.10
Purchase #4	$149.32	4.767%	$156.4381	$156.44	$156.45	$156.40
Purchase #5	$51.91	5.333%	$54.6784	$54.68	$54.70	$54.70
Purchase #6	$64.57	4.422%	$67.4253	$67.43	$67.45	$67.40
Purchase #7	$39.86	9.355%	$43.5889	$43.59	$43.60	$43.60
7 purchase totals =	$469.70		$500.3958	$500.41	$500.50	$500.30