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	$148.90	6.580%	$158.6976	$158.70	$158.70	$158.70
Purchase #2	$158.81	3.225%	$163.9316	$163.93	$163.95	$163.90
Purchase #3	$131.83	4.845%	$138.2172	$138.22	$138.20	$138.20
Purchase #4	$198.39	12.181%	$222.5559	$222.56	$222.55	$222.60
Purchase #5	$74.50	10.815%	$82.5572	$82.56	$82.55	$82.60
Purchase #6	$229.70	5.184%	$241.6076	$241.61	$241.60	$241.60
Purchase #7	$70.26	3.551%	$72.7549	$72.75	$72.75	$72.80
7 purchase totals =	$1,012.39		$1,080.3220	$1,080.33	$1,080.30	$1,080.40