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	$82.41	7.395%	$88.5042	$88.50	$88.50	$88.50
Purchase #2	$221.34	10.513%	$244.6095	$244.61	$244.60	$244.60
Purchase #3	$151.51	6.111%	$160.7688	$160.77	$160.75	$160.80
Purchase #4	$104.53	9.230%	$114.1781	$114.18	$114.20	$114.20
Purchase #5	$143.43	11.406%	$159.7896	$159.79	$159.80	$159.80
Purchase #6	$166.85	4.595%	$174.5168	$174.52	$174.50	$174.50
Purchase #7	$111.70	4.562%	$116.7958	$116.80	$116.80	$116.80
7 purchase totals =	$981.77		$1,059.1628	$1,059.17	$1,059.15	$1,059.20