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	$29.31	8.786%	$31.8852	$31.89	$31.90	$31.90
Purchase #2	$106.85	12.739%	$120.4616	$120.46	$120.45	$120.50
Purchase #3	$218.43	13.497%	$247.9115	$247.91	$247.90	$247.90
Purchase #4	$144.29	10.698%	$159.7261	$159.73	$159.75	$159.70
Purchase #5	$146.69	13.718%	$166.8129	$166.81	$166.80	$166.80
Purchase #6	$212.43	3.806%	$220.5151	$220.52	$220.50	$220.50
Purchase #7	$95.60	13.333%	$108.3463	$108.35	$108.35	$108.30
7 purchase totals =	$953.60		$1,055.6587	$1,055.67	$1,055.65	$1,055.60