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	$83.93	6.495%	$89.3813	$89.38	$89.40	$89.40
Purchase #2	$211.59	13.280%	$239.6892	$239.69	$239.70	$239.70
Purchase #3	$79.83	6.106%	$84.7044	$84.70	$84.70	$84.70
Purchase #4	$230.45	11.244%	$256.3618	$256.36	$256.35	$256.40
Purchase #5	$42.55	11.770%	$47.5581	$47.56	$47.55	$47.60
Purchase #6	$79.87	5.109%	$83.9506	$83.95	$83.95	$84.00
Purchase #7	$100.72	10.718%	$111.5152	$111.52	$111.50	$111.50
7 purchase totals =	$828.94		$913.1606	$913.16	$913.15	$913.30