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	$221.31	11.713%	$247.232	$247.23	$247.25	$247.20
Purchase #2	$39.46	6.699%	$42.1034	$42.10	$42.10	$42.10
Purchase #3	$183.85	11.475%	$204.9468	$204.95	$204.95	$204.90
Purchase #4	$28.50	4.689%	$29.8364	$29.84	$29.85	$29.80
Purchase #5	$209.47	11.466%	$233.4878	$233.49	$233.50	$233.50
Purchase #6	$78.73	6.431%	$83.7931	$83.79	$83.80	$83.80
Purchase #7	$154.69	11.273%	$172.1282	$172.13	$172.15	$172.10
7 purchase totals =	$916.01		$1,013.5277	$1,013.53	$1,013.60	$1,013.40