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	$160.26	12.111%	$179.6691	$179.67	$179.65	$179.70
Purchase #2	$17.26	4.177%	$17.981	$17.98	$18.00	$18.00
Purchase #3	$172.72	11.654%	$192.8488	$192.85	$192.85	$192.80
Purchase #4	$40.96	6.803%	$43.7465	$43.75	$43.75	$43.70
Purchase #5	$96.86	4.218%	$100.9456	$100.95	$100.95	$100.90
Purchase #6	$122.83	4.630%	$128.517	$128.52	$128.50	$128.50
Purchase #7	$105.79	3.188%	$109.1626	$109.16	$109.15	$109.20
7 purchase totals =	$716.68		$772.8706	$772.88	$772.85	$772.80