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	$208.30	12.531%	$234.4021	$234.40	$234.40	$234.40
Purchase #2	$127.43	12.397%	$143.2275	$143.23	$143.25	$143.20
Purchase #3	$120.80	9.674%	$132.4862	$132.49	$132.50	$132.50
Purchase #4	$191.44	7.165%	$205.1567	$205.16	$205.15	$205.20
Purchase #5	$13.93	10.738%	$15.4258	$15.43	$15.45	$15.40
Purchase #6	$103.83	7.824%	$111.9537	$111.95	$111.95	$112.00
Purchase #7	$97.62	3.359%	$100.8991	$100.90	$100.90	$100.90
7 purchase totals =	$863.35		$943.5511	$943.56	$943.60	$943.60