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	$129.41	5.390%	$136.3852	$136.39	$136.40	$136.40
Purchase #2	$175.59	11.861%	$196.4167	$196.42	$196.40	$196.40
Purchase #3	$19.98	8.716%	$21.7215	$21.72	$21.70	$21.70
Purchase #4	$34.77	7.163%	$37.2606	$37.26	$37.25	$37.30
Purchase #5	$106.84	9.282%	$116.7569	$116.76	$116.75	$116.80
Purchase #6	$99.51	13.798%	$113.2404	$113.24	$113.25	$113.20
Purchase #7	$10.78	6.426%	$11.4727	$11.47	$11.45	$11.50
7 purchase totals =	$576.88		$633.2540	$633.26	$633.20	$633.30