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	$17.47	4.643%	$18.2811	$18.28	$18.30	$18.30
Purchase #2	$83.83	4.344%	$87.4716	$87.47	$87.45	$87.50
Purchase #3	$53.60	5.646%	$56.6263	$56.63	$56.65	$56.60
Purchase #4	$123.26	7.490%	$132.4922	$132.49	$132.50	$132.50
Purchase #5	$79.64	3.333%	$82.2944	$82.29	$82.30	$82.30
Purchase #6	$229.54	11.466%	$255.8591	$255.86	$255.85	$255.90
Purchase #7	$186.71	8.865%	$203.2618	$203.26	$203.25	$203.30
7 purchase totals =	$774.05		$836.2865	$836.28	$836.30	$836.40