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	$141.42	6.310%	$150.3436	$150.34	$150.35	$150.30
Purchase #2	$229.89	10.846%	$254.8239	$254.82	$254.80	$254.80
Purchase #3	$150.81	3.693%	$156.3794	$156.38	$156.40	$156.40
Purchase #4	$5.60	11.675%	$6.2538	$6.25	$6.25	$6.30
Purchase #5	$139.97	10.859%	$155.1693	$155.17	$155.15	$155.20
Purchase #6	$229.86	9.725%	$252.2139	$252.21	$252.20	$252.20
Purchase #7	$110.58	11.697%	$123.5145	$123.51	$123.50	$123.50
7 purchase totals =	$1,008.13		$1,098.6984	$1,098.68	$1,098.65	$1,098.70