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	$99.43	11.777%	$111.1399	$111.14	$111.15	$111.10
Purchase #2	$77.67	13.383%	$88.0646	$88.06	$88.05	$88.10
Purchase #3	$164.97	7.661%	$177.6084	$177.61	$177.60	$177.60
Purchase #4	$172.76	9.122%	$188.5192	$188.52	$188.50	$188.50
Purchase #5	$241.25	13.785%	$274.5063	$274.51	$274.50	$274.50
Purchase #6	$248.55	4.267%	$259.1556	$259.16	$259.15	$259.20
Purchase #7	$122.76	9.335%	$134.2196	$134.22	$134.20	$134.20
7 purchase totals =	$1,127.39		$1,233.2136	$1,233.22	$1,233.15	$1,233.20