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	$79.37	6.367%	$84.4235	$84.42	$84.40	$84.40
Purchase #2	$106.81	11.147%	$118.7161	$118.72	$118.70	$118.70
Purchase #3	$107.63	3.408%	$111.298	$111.30	$111.30	$111.30
Purchase #4	$228.37	11.306%	$254.1895	$254.19	$254.20	$254.20
Purchase #5	$181.47	10.330%	$200.2159	$200.22	$200.20	$200.20
Purchase #6	$210.74	5.490%	$222.3096	$222.31	$222.30	$222.30
Purchase #7	$69.89	12.532%	$78.6486	$78.65	$78.65	$78.60
7 purchase totals =	$984.28		$1,069.8012	$1,069.81	$1,069.75	$1,069.70