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	$240.83	6.574%	$256.6622	$256.66	$256.65	$256.70
Purchase #2	$209.78	7.403%	$225.31	$225.31	$225.30	$225.30
Purchase #3	$230.78	7.230%	$247.4654	$247.47	$247.45	$247.50
Purchase #4	$107.71	3.764%	$111.7642	$111.76	$111.75	$111.80
Purchase #5	$161.35	12.647%	$181.7559	$181.76	$181.75	$181.80
Purchase #6	$62.56	13.600%	$71.0682	$71.07	$71.05	$71.10
Purchase #7	$129.61	3.831%	$134.5754	$134.58	$134.60	$134.60
7 purchase totals =	$1,142.62		$1,228.6013	$1,228.61	$1,228.55	$1,228.80