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	$103.88	4.466%	$108.5193	$108.52	$108.50	$108.50
Purchase #2	$199.74	10.761%	$221.234	$221.23	$221.25	$221.20
Purchase #3	$40.86	6.542%	$43.5331	$43.53	$43.55	$43.50
Purchase #4	$102.61	13.331%	$116.2889	$116.29	$116.30	$116.30
Purchase #5	$145.64	9.792%	$159.9011	$159.90	$159.90	$159.90
Purchase #6	$139.25	13.513%	$158.0669	$158.07	$158.05	$158.10
Purchase #7	$24.52	8.122%	$26.5115	$26.51	$26.50	$26.50
7 purchase totals =	$756.50		$834.0548	$834.05	$834.05	$834.00