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	$232.69	11.517%	$259.4889	$259.49	$259.50	$259.50
Purchase #2	$226.67	11.404%	$252.5194	$252.52	$252.50	$252.50
Purchase #3	$185.60	4.691%	$194.3065	$194.31	$194.30	$194.30
Purchase #4	$71.48	9.325%	$78.1455	$78.15	$78.15	$78.10
Purchase #5	$205.67	6.122%	$218.2611	$218.26	$218.25	$218.30
Purchase #6	$19.52	10.699%	$21.6084	$21.61	$21.60	$21.60
Purchase #7	$60.83	13.297%	$68.9186	$68.92	$68.90	$68.90
7 purchase totals =	$1,002.46		$1,093.2484	$1,093.26	$1,093.20	$1,093.20