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	$219.75	12.244%	$246.6562	$246.66	$246.65	$246.70
Purchase #2	$173.89	13.194%	$196.833	$196.83	$196.85	$196.80
Purchase #3	$138.45	12.699%	$156.0318	$156.03	$156.05	$156.00
Purchase #4	$104.31	13.202%	$118.081	$118.08	$118.10	$118.10
Purchase #5	$131.95	8.468%	$143.1235	$143.12	$143.10	$143.10
Purchase #6	$104.56	3.225%	$107.9321	$107.93	$107.95	$107.90
Purchase #7	$37.79	4.870%	$39.6304	$39.63	$39.65	$39.60
7 purchase totals =	$910.70		$1,008.2880	$1,008.28	$1,008.35	$1,008.20