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	$31.51	5.425%	$33.2194	$33.22	$33.20	$33.20
Purchase #2	$120.63	5.700%	$127.5059	$127.51	$127.50	$127.50
Purchase #3	$91.41	10.182%	$100.7174	$100.72	$100.70	$100.70
Purchase #4	$152.47	3.364%	$157.5991	$157.60	$157.60	$157.60
Purchase #5	$80.54	12.335%	$90.4746	$90.47	$90.45	$90.50
Purchase #6	$215.78	8.519%	$234.1623	$234.16	$234.15	$234.20
Purchase #7	$79.81	8.766%	$86.8061	$86.81	$86.80	$86.80
7 purchase totals =	$772.15		$830.4848	$830.49	$830.40	$830.50