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	$199.33	12.680%	$224.605	$224.61	$224.60	$224.60
Purchase #2	$90.66	9.683%	$99.4386	$99.44	$99.45	$99.40
Purchase #3	$74.25	4.822%	$77.8303	$77.83	$77.85	$77.80
Purchase #4	$49.76	12.800%	$56.1293	$56.13	$56.15	$56.10
Purchase #5	$50.57	12.451%	$56.8665	$56.87	$56.85	$56.90
Purchase #6	$211.88	4.340%	$221.0756	$221.08	$221.10	$221.10
Purchase #7	$26.33	9.692%	$28.8819	$28.88	$28.90	$28.90
7 purchase totals =	$702.78		$764.8272	$764.84	$764.90	$764.80