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	$38.57	12.341%	$43.3299	$43.33	$43.35	$43.30
Purchase #2	$100.97	10.159%	$111.2275	$111.23	$111.25	$111.20
Purchase #3	$198.29	10.160%	$218.4363	$218.44	$218.45	$218.40
Purchase #4	$16.86	5.122%	$17.7236	$17.72	$17.70	$17.70
Purchase #5	$43.86	12.806%	$49.4767	$49.48	$49.50	$49.50
Purchase #6	$184.66	5.343%	$194.5264	$194.53	$194.55	$194.50
Purchase #7	$18.81	4.105%	$19.5822	$19.58	$19.60	$19.60
7 purchase totals =	$602.02		$654.3026	$654.31	$654.40	$654.20