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	$86.70	4.411%	$90.5243	$90.52	$90.50	$90.50
Purchase #2	$239.52	13.180%	$271.0887	$271.09	$271.10	$271.10
Purchase #3	$162.44	10.205%	$179.017	$179.02	$179.00	$179.00
Purchase #4	$158.29	3.530%	$163.8776	$163.88	$163.90	$163.90
Purchase #5	$98.69	4.624%	$103.2534	$103.25	$103.25	$103.30
Purchase #6	$139.83	3.184%	$144.2822	$144.28	$144.30	$144.30
Purchase #7	$236.61	12.281%	$265.6681	$265.67	$265.65	$265.70
7 purchase totals =	$1,122.08		$1,217.7113	$1,217.71	$1,217.70	$1,217.80