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	$246.90	9.814%	$271.1308	$271.13	$271.15	$271.10
Purchase #2	$116.82	8.304%	$126.5207	$126.52	$126.50	$126.50
Purchase #3	$190.39	9.621%	$208.7074	$208.71	$208.70	$208.70
Purchase #4	$88.40	4.244%	$92.1517	$92.15	$92.15	$92.20
Purchase #5	$148.88	3.650%	$154.3141	$154.31	$154.30	$154.30
Purchase #6	$177.55	8.303%	$192.292	$192.29	$192.30	$192.30
Purchase #7	$111.74	13.770%	$127.1266	$127.13	$127.15	$127.10
7 purchase totals =	$1,080.68		$1,172.2433	$1,172.24	$1,172.25	$1,172.20