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	$188.56	4.149%	$196.3834	$196.38	$196.40	$196.40
Purchase #2	$128.31	11.867%	$143.5365	$143.54	$143.55	$143.50
Purchase #3	$232.27	11.335%	$258.5978	$258.60	$258.60	$258.60
Purchase #4	$16.62	11.174%	$18.4771	$18.48	$18.50	$18.50
Purchase #5	$116.64	4.174%	$121.5086	$121.51	$121.50	$121.50
Purchase #6	$147.76	7.324%	$158.5819	$158.58	$158.60	$158.60
Purchase #7	$214.88	12.277%	$241.2608	$241.26	$241.25	$241.30
7 purchase totals =	$1,045.04		$1,138.3461	$1,138.35	$1,138.40	$1,138.40