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	$118.75	8.198%	$128.4851	$128.49	$128.50	$128.50
Purchase #2	$202.78	7.276%	$217.5343	$217.53	$217.55	$217.50
Purchase #3	$200.93	10.788%	$222.6063	$222.61	$222.60	$222.60
Purchase #4	$151.55	12.720%	$170.8272	$170.83	$170.85	$170.80
Purchase #5	$70.68	3.597%	$73.2224	$73.22	$73.20	$73.20
Purchase #6	$123.51	3.815%	$128.2219	$128.22	$128.20	$128.20
Purchase #7	$116.27	6.472%	$123.795	$123.80	$123.80	$123.80
7 purchase totals =	$984.47		$1,064.6922	$1,064.70	$1,064.70	$1,064.60