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	$11.68	7.667%	$12.5755	$12.58	$12.60	$12.60
Purchase #2	$228.66	5.825%	$241.9794	$241.98	$242.00	$242.00
Purchase #3	$34.64	12.168%	$38.855	$38.86	$38.85	$38.90
Purchase #4	$77.25	7.337%	$82.9178	$82.92	$82.90	$82.90
Purchase #5	$60.93	13.116%	$68.9216	$68.92	$68.90	$68.90
Purchase #6	$186.59	5.452%	$196.7629	$196.76	$196.75	$196.80
Purchase #7	$91.77	8.601%	$99.6631	$99.66	$99.65	$99.70
7 purchase totals =	$691.52		$741.6753	$741.68	$741.65	$741.80