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	$134.88	11.392%	$150.2455	$150.25	$150.25	$150.20
Purchase #2	$97.61	13.862%	$111.1407	$111.14	$111.15	$111.10
Purchase #3	$42.49	5.103%	$44.6583	$44.66	$44.65	$44.70
Purchase #4	$144.55	3.866%	$150.1383	$150.14	$150.15	$150.10
Purchase #5	$31.67	7.461%	$34.0329	$34.03	$34.05	$34.00
Purchase #6	$243.75	4.795%	$255.4378	$255.44	$255.45	$255.40
Purchase #7	$111.41	8.154%	$120.4944	$120.49	$120.50	$120.50
7 purchase totals =	$806.36		$866.1479	$866.15	$866.20	$866.00