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	$241.69	7.293%	$259.3165	$259.32	$259.30	$259.30
Purchase #2	$71.84	8.840%	$78.1907	$78.19	$78.20	$78.20
Purchase #3	$165.38	9.233%	$180.6495	$180.65	$180.65	$180.60
Purchase #4	$222.71	3.494%	$230.4915	$230.49	$230.50	$230.50
Purchase #5	$220.44	7.325%	$236.5872	$236.59	$236.60	$236.60
Purchase #6	$74.85	5.396%	$78.8889	$78.89	$78.90	$78.90
Purchase #7	$73.52	11.730%	$82.1439	$82.14	$82.15	$82.10
7 purchase totals =	$1,070.43		$1,146.2682	$1,146.27	$1,146.30	$1,146.20