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	$100.31	11.334%	$111.6791	$111.68	$111.70	$111.70
Purchase #2	$176.35	7.686%	$189.9043	$189.90	$189.90	$189.90
Purchase #3	$214.28	13.172%	$242.505	$242.51	$242.50	$242.50
Purchase #4	$138.82	11.285%	$154.4858	$154.49	$154.50	$154.50
Purchase #5	$184.74	10.487%	$204.1137	$204.11	$204.10	$204.10
Purchase #6	$75.95	4.638%	$79.4726	$79.47	$79.45	$79.50
Purchase #7	$98.61	5.511%	$104.0444	$104.04	$104.05	$104.00
7 purchase totals =	$989.06		$1,086.2049	$1,086.20	$1,086.20	$1,086.20