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	$28.40	13.716%	$32.2953	$32.30	$32.30	$32.30
Purchase #2	$114.98	4.169%	$119.7735	$119.77	$119.75	$119.80
Purchase #3	$155.85	11.263%	$173.4034	$173.40	$173.40	$173.40
Purchase #4	$110.93	4.625%	$116.0605	$116.06	$116.05	$116.10
Purchase #5	$244.61	4.782%	$256.3073	$256.31	$256.30	$256.30
Purchase #6	$73.97	3.648%	$76.6684	$76.67	$76.65	$76.70
Purchase #7	$104.64	6.547%	$111.4908	$111.49	$111.50	$111.50
7 purchase totals =	$833.38		$885.9992	$886.00	$885.95	$886.10