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	$154.85	4.721%	$162.1605	$162.16	$162.15	$162.20
Purchase #2	$148.67	6.572%	$158.4406	$158.44	$158.45	$158.40
Purchase #3	$29.75	8.376%	$32.2419	$32.24	$32.25	$32.20
Purchase #4	$183.52	8.680%	$199.4495	$199.45	$199.45	$199.40
Purchase #5	$96.75	10.449%	$106.8594	$106.86	$106.85	$106.90
Purchase #6	$195.65	12.200%	$219.5193	$219.52	$219.50	$219.50
Purchase #7	$16.59	13.721%	$18.8663	$18.87	$18.85	$18.90
7 purchase totals =	$825.78		$897.5375	$897.54	$897.50	$897.50