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	$141.34	11.865%	$158.11	$158.11	$158.10	$158.10
Purchase #2	$89.72	3.799%	$93.1285	$93.13	$93.15	$93.10
Purchase #3	$110.65	11.217%	$123.0616	$123.06	$123.05	$123.10
Purchase #4	$91.60	8.697%	$99.5665	$99.57	$99.55	$99.60
Purchase #5	$214.70	6.186%	$227.9813	$227.98	$228.00	$228.00
Purchase #6	$128.95	12.521%	$145.0958	$145.10	$145.10	$145.10
Purchase #7	$214.98	8.787%	$233.8703	$233.87	$233.85	$233.90
7 purchase totals =	$991.94		$1,080.8140	$1,080.82	$1,080.80	$1,080.90