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	$104.31	13.658%	$118.5567	$118.56	$118.55	$118.60
Purchase #2	$155.44	6.613%	$165.7192	$165.72	$165.70	$165.70
Purchase #3	$214.61	8.509%	$232.8712	$232.87	$232.85	$232.90
Purchase #4	$54.52	5.525%	$57.5322	$57.53	$57.55	$57.50
Purchase #5	$240.52	13.326%	$272.5717	$272.57	$272.55	$272.60
Purchase #6	$80.32	3.788%	$83.3625	$83.36	$83.35	$83.40
Purchase #7	$116.89	10.244%	$128.8642	$128.86	$128.85	$128.90
7 purchase totals =	$966.61		$1,059.4777	$1,059.47	$1,059.40	$1,059.60