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	$59.52	11.858%	$66.5779	$66.58	$66.60	$66.60
Purchase #2	$155.90	9.503%	$170.7152	$170.72	$170.70	$170.70
Purchase #3	$134.29	6.359%	$142.8295	$142.83	$142.85	$142.80
Purchase #4	$77.50	12.838%	$87.4495	$87.45	$87.45	$87.40
Purchase #5	$200.79	3.675%	$208.169	$208.17	$208.15	$208.20
Purchase #6	$118.80	7.133%	$127.274	$127.27	$127.25	$127.30
Purchase #7	$185.79	13.346%	$210.5855	$210.59	$210.60	$210.60
7 purchase totals =	$932.59		$1,013.6006	$1,013.61	$1,013.60	$1,013.60