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	$189.28	13.173%	$214.2139	$214.21	$214.20	$214.20
Purchase #2	$132.85	6.700%	$141.751	$141.75	$141.75	$141.80
Purchase #3	$78.41	9.260%	$85.6708	$85.67	$85.65	$85.70
Purchase #4	$173.93	10.287%	$191.8222	$191.82	$191.80	$191.80
Purchase #5	$126.47	6.151%	$134.2492	$134.25	$134.25	$134.20
Purchase #6	$153.60	3.443%	$158.8884	$158.89	$158.90	$158.90
Purchase #7	$229.48	10.759%	$254.1698	$254.17	$254.15	$254.20
7 purchase totals =	$1,084.02		$1,180.7653	$1,180.76	$1,180.70	$1,180.80