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	$238.62	8.870%	$259.7856	$259.79	$259.80	$259.80
Purchase #2	$166.53	7.216%	$178.5468	$178.55	$178.55	$178.50
Purchase #3	$102.27	10.347%	$112.8519	$112.85	$112.85	$112.90
Purchase #4	$77.89	12.579%	$87.6878	$87.69	$87.70	$87.70
Purchase #5	$167.52	10.131%	$184.4915	$184.49	$184.50	$184.50
Purchase #6	$167.32	3.449%	$173.0909	$173.09	$173.10	$173.10
Purchase #7	$134.55	6.391%	$143.1491	$143.15	$143.15	$143.10
7 purchase totals =	$1,054.70		$1,139.6036	$1,139.61	$1,139.65	$1,139.60