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	$46.68	11.657%	$52.1215	$52.12	$52.10	$52.10
Purchase #2	$228.55	10.174%	$251.8027	$251.80	$251.80	$251.80
Purchase #3	$183.31	12.321%	$205.8956	$205.90	$205.90	$205.90
Purchase #4	$117.45	8.529%	$127.4673	$127.47	$127.45	$127.50
Purchase #5	$192.43	3.727%	$199.6019	$199.60	$199.60	$199.60
Purchase #6	$67.92	5.581%	$71.7106	$71.71	$71.70	$71.70
Purchase #7	$170.67	11.802%	$190.8125	$190.81	$190.80	$190.80
7 purchase totals =	$1,007.01		$1,099.4121	$1,099.41	$1,099.35	$1,099.40