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	$44.34	12.109%	$49.7091	$49.71	$49.70	$49.70
Purchase #2	$157.63	4.676%	$165.0008	$165.00	$165.00	$165.00
Purchase #3	$239.78	7.325%	$257.3439	$257.34	$257.35	$257.30
Purchase #4	$95.53	10.180%	$105.255	$105.26	$105.25	$105.30
Purchase #5	$152.50	8.418%	$165.3375	$165.34	$165.35	$165.30
Purchase #6	$123.88	11.115%	$137.6493	$137.65	$137.65	$137.60
Purchase #7	$98.86	12.670%	$111.3856	$111.39	$111.40	$111.40
7 purchase totals =	$912.52		$991.6812	$991.69	$991.70	$991.60