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	$37.41	4.468%	$39.0815	$39.08	$39.10	$39.10
Purchase #2	$118.81	7.478%	$127.6946	$127.69	$127.70	$127.70
Purchase #3	$96.95	3.299%	$100.1484	$100.15	$100.15	$100.10
Purchase #4	$158.93	11.648%	$177.4422	$177.44	$177.45	$177.40
Purchase #5	$39.35	11.634%	$43.928	$43.93	$43.95	$43.90
Purchase #6	$57.32	6.189%	$60.8675	$60.87	$60.85	$60.90
Purchase #7	$44.89	8.146%	$48.5467	$48.55	$48.55	$48.50
7 purchase totals =	$553.66		$597.7089	$597.71	$597.75	$597.60