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	$118.90	9.670%	$130.3976	$130.40	$130.40	$130.40
Purchase #2	$120.30	13.422%	$136.4467	$136.45	$136.45	$136.40
Purchase #3	$193.67	13.197%	$219.2286	$219.23	$219.25	$219.20
Purchase #4	$79.83	4.501%	$83.4231	$83.42	$83.40	$83.40
Purchase #5	$93.87	11.341%	$104.5158	$104.52	$104.50	$104.50
Purchase #6	$82.62	3.472%	$85.4886	$85.49	$85.50	$85.50
Purchase #7	$143.77	7.370%	$154.3658	$154.37	$154.35	$154.40
7 purchase totals =	$832.96		$913.8662	$913.88	$913.85	$913.80