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	$16.88	6.873%	$18.0402	$18.04	$18.05	$18.00
Purchase #2	$62.75	6.665%	$66.9323	$66.93	$66.95	$66.90
Purchase #3	$206.65	7.689%	$222.5393	$222.54	$222.55	$222.50
Purchase #4	$198.85	13.103%	$224.9053	$224.91	$224.90	$224.90
Purchase #5	$56.71	6.270%	$60.2657	$60.27	$60.25	$60.30
Purchase #6	$217.55	9.795%	$238.859	$238.86	$238.85	$238.90
Purchase #7	$228.81	4.714%	$239.5961	$239.60	$239.60	$239.60
7 purchase totals =	$988.20		$1,071.1379	$1,071.15	$1,071.15	$1,071.10