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	$99.59	10.291%	$109.8388	$109.84	$109.85	$109.80
Purchase #2	$156.95	10.142%	$172.8679	$172.87	$172.85	$172.90
Purchase #3	$230.25	11.555%	$256.8554	$256.86	$256.85	$256.90
Purchase #4	$177.83	10.105%	$195.7997	$195.80	$195.80	$195.80
Purchase #5	$6.47	5.730%	$6.8407	$6.84	$6.85	$6.80
Purchase #6	$139.63	13.370%	$158.2985	$158.30	$158.30	$158.30
Purchase #7	$64.89	5.406%	$68.398	$68.40	$68.40	$68.40
7 purchase totals =	$875.61		$968.8990	$968.91	$968.90	$968.90