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	$220.55	4.814%	$231.1673	$231.17	$231.15	$231.20
Purchase #2	$242.44	11.210%	$269.6175	$269.62	$269.60	$269.60
Purchase #3	$177.77	4.329%	$185.4657	$185.47	$185.45	$185.50
Purchase #4	$174.98	12.408%	$196.6915	$196.69	$196.70	$196.70
Purchase #5	$104.52	13.527%	$118.6584	$118.66	$118.65	$118.70
Purchase #6	$58.48	10.461%	$64.5976	$64.60	$64.60	$64.60
Purchase #7	$103.45	10.229%	$114.0319	$114.03	$114.05	$114.00
7 purchase totals =	$1,082.19		$1,180.2299	$1,180.24	$1,180.20	$1,180.30