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	$30.54	7.336%	$32.7804	$32.78	$32.80	$32.80
Purchase #2	$90.82	9.543%	$99.487	$99.49	$99.50	$99.50
Purchase #3	$234.34	8.170%	$253.4856	$253.49	$253.50	$253.50
Purchase #4	$16.30	10.732%	$18.0493	$18.05	$18.05	$18.00
Purchase #5	$101.28	4.580%	$105.9186	$105.92	$105.90	$105.90
Purchase #6	$65.79	13.363%	$74.5815	$74.58	$74.60	$74.60
Purchase #7	$59.87	4.665%	$62.6629	$62.66	$62.65	$62.70
7 purchase totals =	$598.94		$646.9653	$646.97	$647.00	$647.00