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	$85.30	6.463%	$90.8129	$90.81	$90.80	$90.80
Purchase #2	$150.57	7.230%	$161.4562	$161.46	$161.45	$161.50
Purchase #3	$198.60	3.458%	$205.4676	$205.47	$205.45	$205.50
Purchase #4	$217.54	11.268%	$242.0524	$242.05	$242.05	$242.10
Purchase #5	$172.94	6.486%	$184.1569	$184.16	$184.15	$184.20
Purchase #6	$89.30	12.846%	$100.7715	$100.77	$100.75	$100.80
Purchase #7	$130.93	5.610%	$138.2752	$138.28	$138.30	$138.30
7 purchase totals =	$1,045.18		$1,122.9927	$1,123.00	$1,122.95	$1,123.20