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	$123.32	13.301%	$139.7228	$139.72	$139.70	$139.70
Purchase #2	$96.93	7.602%	$104.2986	$104.30	$104.30	$104.30
Purchase #3	$237.43	7.162%	$254.4347	$254.43	$254.45	$254.40
Purchase #4	$59.84	11.770%	$66.8832	$66.88	$66.90	$66.90
Purchase #5	$173.52	10.779%	$192.2237	$192.22	$192.20	$192.20
Purchase #6	$52.88	8.523%	$57.387	$57.39	$57.40	$57.40
Purchase #7	$210.89	13.249%	$238.8308	$238.83	$238.85	$238.80
7 purchase totals =	$954.81		$1,053.7808	$1,053.77	$1,053.80	$1,053.70