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	$60.26	9.324%	$65.8786	$65.88	$65.90	$65.90
Purchase #2	$105.54	10.700%	$116.8328	$116.83	$116.85	$116.80
Purchase #3	$121.56	12.615%	$136.8948	$136.89	$136.90	$136.90
Purchase #4	$53.37	11.847%	$59.6927	$59.69	$59.70	$59.70
Purchase #5	$105.78	5.561%	$111.6624	$111.66	$111.65	$111.70
Purchase #6	$45.79	3.677%	$47.4737	$47.47	$47.45	$47.50
Purchase #7	$46.68	4.322%	$48.6975	$48.70	$48.70	$48.70
7 purchase totals =	$538.98		$587.1325	$587.12	$587.15	$587.20