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	$28.91	5.724%	$30.5648	$30.56	$30.55	$30.60
Purchase #2	$38.94	11.623%	$43.466	$43.47	$43.45	$43.50
Purchase #3	$24.74	11.467%	$27.5769	$27.58	$27.60	$27.60
Purchase #4	$111.78	10.395%	$123.3995	$123.40	$123.40	$123.40
Purchase #5	$65.91	8.302%	$71.3818	$71.38	$71.40	$71.40
Purchase #6	$234.45	9.505%	$256.7345	$256.73	$256.75	$256.70
Purchase #7	$130.65	11.385%	$145.5245	$145.52	$145.50	$145.50
7 purchase totals =	$635.38		$698.6480	$698.64	$698.65	$698.70