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	$149.45	10.131%	$164.5908	$164.59	$164.60	$164.60
Purchase #2	$172.52	8.325%	$186.8823	$186.88	$186.90	$186.90
Purchase #3	$222.30	13.120%	$251.4658	$251.47	$251.45	$251.50
Purchase #4	$51.61	6.110%	$54.7634	$54.76	$54.75	$54.80
Purchase #5	$132.72	6.610%	$141.4928	$141.49	$141.50	$141.50
Purchase #6	$63.39	4.737%	$66.3928	$66.39	$66.40	$66.40
Purchase #7	$124.65	7.697%	$134.2443	$134.24	$134.25	$134.20
7 purchase totals =	$916.64		$999.8322	$999.82	$999.85	$999.90