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	$38.42	4.495%	$40.147	$40.15	$40.15	$40.10
Purchase #2	$127.94	8.722%	$139.0989	$139.10	$139.10	$139.10
Purchase #3	$160.97	13.832%	$183.2354	$183.24	$183.25	$183.20
Purchase #4	$75.37	6.659%	$80.3889	$80.39	$80.40	$80.40
Purchase #5	$108.31	7.165%	$116.0704	$116.07	$116.05	$116.10
Purchase #6	$168.58	10.102%	$185.61	$185.61	$185.60	$185.60
Purchase #7	$222.87	8.249%	$241.2545	$241.25	$241.25	$241.30
7 purchase totals =	$902.46		$985.8051	$985.81	$985.80	$985.80