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	$100.32	10.749%	$111.1034	$111.10	$111.10	$111.10
Purchase #2	$140.45	3.569%	$145.4627	$145.46	$145.45	$145.50
Purchase #3	$17.86	11.341%	$19.8855	$19.89	$19.90	$19.90
Purchase #4	$57.85	7.454%	$62.1621	$62.16	$62.15	$62.20
Purchase #5	$65.73	8.252%	$71.154	$71.15	$71.15	$71.20
Purchase #6	$122.53	4.403%	$127.925	$127.93	$127.95	$127.90
Purchase #7	$57.46	4.854%	$60.2491	$60.25	$60.25	$60.20
7 purchase totals =	$562.20		$597.9418	$597.94	$597.95	$598.00