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	$184.83	13.390%	$209.5787	$209.58	$209.60	$209.60
Purchase #2	$53.98	9.638%	$59.1826	$59.18	$59.20	$59.20
Purchase #3	$172.95	3.797%	$179.5169	$179.52	$179.50	$179.50
Purchase #4	$89.26	5.723%	$94.3683	$94.37	$94.35	$94.40
Purchase #5	$158.91	12.634%	$178.9867	$178.99	$179.00	$179.00
Purchase #6	$187.47	5.583%	$197.9365	$197.94	$197.95	$197.90
Purchase #7	$85.71	11.522%	$95.5855	$95.59	$95.60	$95.60
7 purchase totals =	$933.11		$1,015.1552	$1,015.17	$1,015.20	$1,015.20