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	$92.51	13.753%	$105.2329	$105.23	$105.25	$105.20
Purchase #2	$203.76	13.313%	$230.8866	$230.89	$230.90	$230.90
Purchase #3	$74.96	10.449%	$82.7926	$82.79	$82.80	$82.80
Purchase #4	$60.43	4.327%	$63.0448	$63.04	$63.05	$63.00
Purchase #5	$151.30	6.239%	$160.7396	$160.74	$160.75	$160.70
Purchase #6	$40.79	3.384%	$42.1703	$42.17	$42.15	$42.20
Purchase #7	$36.75	3.516%	$38.0421	$38.04	$38.05	$38.00
7 purchase totals =	$660.50		$722.9089	$722.90	$722.95	$722.80