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	$153.85	7.429%	$165.2795	$165.28	$165.30	$165.30
Purchase #2	$74.74	5.625%	$78.9441	$78.94	$78.95	$78.90
Purchase #3	$137.70	3.719%	$142.8211	$142.82	$142.80	$142.80
Purchase #4	$34.98	10.313%	$38.5875	$38.59	$38.60	$38.60
Purchase #5	$50.60	6.367%	$53.8217	$53.82	$53.80	$53.80
Purchase #6	$126.92	3.198%	$130.9789	$130.98	$131.00	$131.00
Purchase #7	$188.42	8.236%	$203.9383	$203.94	$203.95	$203.90
7 purchase totals =	$767.21		$814.3711	$814.37	$814.40	$814.30