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	$21.98	11.558%	$24.5204	$24.52	$24.50	$24.50
Purchase #2	$183.45	11.516%	$204.5761	$204.58	$204.60	$204.60
Purchase #3	$69.30	4.636%	$72.5127	$72.51	$72.50	$72.50
Purchase #4	$21.49	5.722%	$22.7197	$22.72	$22.70	$22.70
Purchase #5	$66.40	6.720%	$70.8621	$70.86	$70.85	$70.90
Purchase #6	$19.62	5.190%	$20.6383	$20.64	$20.65	$20.60
Purchase #7	$117.60	11.523%	$131.151	$131.15	$131.15	$131.20
7 purchase totals =	$499.84		$546.9803	$546.98	$546.95	$547.00