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	$15.61	13.365%	$17.6963	$17.70	$17.70	$17.70
Purchase #2	$65.68	7.781%	$70.7906	$70.79	$70.80	$70.80
Purchase #3	$60.27	12.334%	$67.7037	$67.70	$67.70	$67.70
Purchase #4	$105.32	6.204%	$111.8541	$111.85	$111.85	$111.90
Purchase #5	$128.32	7.337%	$137.7348	$137.73	$137.75	$137.70
Purchase #6	$107.36	4.593%	$112.291	$112.29	$112.30	$112.30
Purchase #7	$130.63	10.217%	$143.9765	$143.98	$144.00	$144.00
7 purchase totals =	$613.19		$662.0470	$662.04	$662.10	$662.10