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	$246.82	9.228%	$269.5965	$269.60	$269.60	$269.60
Purchase #2	$37.71	6.724%	$40.2456	$40.25	$40.25	$40.20
Purchase #3	$250.65	13.607%	$284.7559	$284.76	$284.75	$284.80
Purchase #4	$180.45	13.800%	$205.3521	$205.35	$205.35	$205.40
Purchase #5	$96.70	4.285%	$100.8436	$100.84	$100.85	$100.80
Purchase #6	$65.27	7.641%	$70.2573	$70.26	$70.25	$70.30
Purchase #7	$17.86	4.181%	$18.6067	$18.61	$18.60	$18.60
7 purchase totals =	$895.46		$989.6577	$989.67	$989.65	$989.70