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	$100.50	13.683%	$114.2514	$114.25	$114.25	$114.30
Purchase #2	$13.50	8.255%	$14.6144	$14.61	$14.60	$14.60
Purchase #3	$171.78	11.874%	$192.1772	$192.18	$192.20	$192.20
Purchase #4	$116.36	11.309%	$129.5192	$129.52	$129.50	$129.50
Purchase #5	$143.83	3.175%	$148.3966	$148.40	$148.40	$148.40
Purchase #6	$47.25	6.604%	$50.3704	$50.37	$50.35	$50.40
Purchase #7	$109.71	12.401%	$123.3151	$123.32	$123.30	$123.30
7 purchase totals =	$702.93		$772.6443	$772.65	$772.60	$772.70