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	$116.58	6.466%	$124.1181	$124.12	$124.10	$124.10
Purchase #2	$74.32	4.819%	$77.9015	$77.90	$77.90	$77.90
Purchase #3	$123.87	5.381%	$130.5354	$130.54	$130.55	$130.50
Purchase #4	$33.84	3.277%	$34.9489	$34.95	$34.95	$34.90
Purchase #5	$145.40	9.316%	$158.9455	$158.95	$158.95	$158.90
Purchase #6	$79.55	13.549%	$90.3282	$90.33	$90.35	$90.30
Purchase #7	$42.39	3.337%	$43.8046	$43.80	$43.80	$43.80
7 purchase totals =	$615.95		$660.5822	$660.59	$660.60	$660.40