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	$155.83	11.341%	$173.5027	$173.50	$173.50	$173.50
Purchase #2	$212.74	4.168%	$221.607	$221.61	$221.60	$221.60
Purchase #3	$133.86	4.154%	$139.4205	$139.42	$139.40	$139.40
Purchase #4	$199.73	8.769%	$217.2443	$217.24	$217.25	$217.20
Purchase #5	$147.70	7.257%	$158.4186	$158.42	$158.40	$158.40
Purchase #6	$13.96	13.104%	$15.7893	$15.79	$15.80	$15.80
Purchase #7	$38.77	10.214%	$42.73	$42.73	$42.75	$42.70
7 purchase totals =	$902.59		$968.7124	$968.71	$968.70	$968.60