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	$13.75	13.347%	$15.5852	$15.59	$15.60	$15.60
Purchase #2	$211.54	13.863%	$240.8658	$240.87	$240.85	$240.90
Purchase #3	$108.70	5.265%	$114.4231	$114.42	$114.40	$114.40
Purchase #4	$153.43	7.628%	$165.1336	$165.13	$165.15	$165.10
Purchase #5	$57.37	5.523%	$60.5385	$60.54	$60.55	$60.50
Purchase #6	$195.58	12.533%	$220.092	$220.09	$220.10	$220.10
Purchase #7	$176.86	5.105%	$185.8887	$185.89	$185.90	$185.90
7 purchase totals =	$917.23		$1,002.5269	$1,002.53	$1,002.55	$1,002.50