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	$27.40	5.296%	$28.8511	$28.85	$28.85	$28.90
Purchase #2	$62.90	5.680%	$66.4727	$66.47	$66.45	$66.50
Purchase #3	$188.38	6.114%	$199.8976	$199.90	$199.90	$199.90
Purchase #4	$19.51	13.265%	$22.098	$22.10	$22.10	$22.10
Purchase #5	$141.82	12.816%	$159.9957	$160.00	$160.00	$160.00
Purchase #6	$194.59	7.823%	$209.8128	$209.81	$209.80	$209.80
Purchase #7	$11.60	8.594%	$12.5969	$12.60	$12.60	$12.60
7 purchase totals =	$646.20		$699.7248	$699.73	$699.70	$699.80