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	$158.96	10.398%	$175.4887	$175.49	$175.50	$175.50
Purchase #2	$199.56	3.528%	$206.6005	$206.60	$206.60	$206.60
Purchase #3	$48.80	6.702%	$52.0706	$52.07	$52.05	$52.10
Purchase #4	$13.88	6.789%	$14.8223	$14.82	$14.80	$14.80
Purchase #5	$45.64	8.872%	$49.6892	$49.69	$49.70	$49.70
Purchase #6	$36.70	7.863%	$39.5857	$39.59	$39.60	$39.60
Purchase #7	$105.39	5.808%	$111.5111	$111.51	$111.50	$111.50
7 purchase totals =	$608.93		$649.7681	$649.77	$649.75	$649.80