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	$10.25	4.536%	$10.7149	$10.71	$10.70	$10.70
Purchase #2	$138.71	7.218%	$148.7221	$148.72	$148.70	$148.70
Purchase #3	$106.60	4.643%	$111.5494	$111.55	$111.55	$111.50
Purchase #4	$139.62	5.165%	$146.8314	$146.83	$146.85	$146.80
Purchase #5	$29.80	13.774%	$33.9047	$33.90	$33.90	$33.90
Purchase #6	$64.35	13.642%	$73.1286	$73.13	$73.15	$73.10
Purchase #7	$202.92	7.634%	$218.4109	$218.41	$218.40	$218.40
7 purchase totals =	$692.25		$743.2620	$743.25	$743.25	$743.10