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	$29.72	13.711%	$33.7949	$33.79	$33.80	$33.80
Purchase #2	$235.54	4.737%	$246.6975	$246.70	$246.70	$246.70
Purchase #3	$48.48	4.233%	$50.5322	$50.53	$50.55	$50.50
Purchase #4	$15.31	11.654%	$17.0942	$17.09	$17.10	$17.10
Purchase #5	$50.76	6.545%	$54.0822	$54.08	$54.10	$54.10
Purchase #6	$106.30	5.826%	$112.493	$112.49	$112.50	$112.50
Purchase #7	$88.33	13.869%	$100.5805	$100.58	$100.60	$100.60
7 purchase totals =	$574.44		$615.2745	$615.26	$615.35	$615.30