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	$95.53	12.534%	$107.5037	$107.50	$107.50	$107.50
Purchase #2	$118.56	13.622%	$134.7102	$134.71	$134.70	$134.70
Purchase #3	$96.76	4.321%	$100.941	$100.94	$100.95	$100.90
Purchase #4	$209.78	4.707%	$219.6543	$219.65	$219.65	$219.70
Purchase #5	$206.40	4.514%	$215.7169	$215.72	$215.70	$215.70
Purchase #6	$14.25	3.393%	$14.7335	$14.73	$14.75	$14.70
Purchase #7	$37.39	10.587%	$41.3485	$41.35	$41.35	$41.30
7 purchase totals =	$778.67		$834.6081	$834.60	$834.60	$834.50