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	$16.28	13.339%	$18.4516	$18.45	$18.45	$18.50
Purchase #2	$90.88	10.346%	$100.2824	$100.28	$100.30	$100.30
Purchase #3	$153.27	6.560%	$163.3245	$163.32	$163.30	$163.30
Purchase #4	$180.60	7.153%	$193.5183	$193.52	$193.50	$193.50
Purchase #5	$39.58	11.225%	$44.0229	$44.02	$44.00	$44.00
Purchase #6	$74.76	5.591%	$78.9398	$78.94	$78.95	$78.90
Purchase #7	$29.39	11.478%	$32.7634	$32.76	$32.75	$32.80
7 purchase totals =	$584.76		$631.3029	$631.29	$631.25	$631.30