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	$240.85	6.581%	$256.7003	$256.70	$256.70	$256.70
Purchase #2	$236.25	3.304%	$244.0557	$244.06	$244.05	$244.10
Purchase #3	$106.45	9.648%	$116.7203	$116.72	$116.70	$116.70
Purchase #4	$55.53	3.393%	$57.4141	$57.41	$57.40	$57.40
Purchase #5	$46.66	8.205%	$50.4885	$50.49	$50.50	$50.50
Purchase #6	$209.58	12.274%	$235.3038	$235.30	$235.30	$235.30
Purchase #7	$54.58	4.180%	$56.8614	$56.86	$56.85	$56.90
7 purchase totals =	$949.90		$1,017.5441	$1,017.54	$1,017.50	$1,017.60