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	$180.81	9.849%	$198.618	$198.62	$198.60	$198.60
Purchase #2	$49.65	13.333%	$56.2698	$56.27	$56.25	$56.30
Purchase #3	$71.47	8.396%	$77.4706	$77.47	$77.45	$77.50
Purchase #4	$161.50	12.159%	$181.1368	$181.14	$181.15	$181.10
Purchase #5	$174.40	6.379%	$185.525	$185.53	$185.55	$185.50
Purchase #6	$42.91	12.180%	$48.1364	$48.14	$48.15	$48.10
Purchase #7	$139.63	4.398%	$145.7709	$145.77	$145.75	$145.80
7 purchase totals =	$820.37		$892.9275	$892.94	$892.90	$892.90