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	$49.95	3.737%	$51.8166	$51.82	$51.80	$51.80
Purchase #2	$88.47	13.604%	$100.5055	$100.51	$100.50	$100.50
Purchase #3	$203.88	13.250%	$230.8941	$230.89	$230.90	$230.90
Purchase #4	$8.32	8.144%	$8.9976	$9.00	$9.00	$9.00
Purchase #5	$114.87	10.604%	$127.0508	$127.05	$127.05	$127.10
Purchase #6	$186.68	12.771%	$210.5209	$210.52	$210.50	$210.50
Purchase #7	$196.25	6.182%	$208.3822	$208.38	$208.40	$208.40
7 purchase totals =	$848.42		$938.1677	$938.17	$938.15	$938.20