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	$66.29	7.750%	$71.4275	$71.43	$71.45	$71.40
Purchase #2	$218.30	5.533%	$230.3785	$230.38	$230.40	$230.40
Purchase #3	$133.41	8.146%	$144.2776	$144.28	$144.30	$144.30
Purchase #4	$116.66	3.358%	$120.5774	$120.58	$120.60	$120.60
Purchase #5	$216.58	6.589%	$230.8505	$230.85	$230.85	$230.90
Purchase #6	$213.59	3.852%	$221.8175	$221.82	$221.80	$221.80
Purchase #7	$11.93	4.704%	$12.4912	$12.49	$12.50	$12.50
7 purchase totals =	$976.76		$1,031.8202	$1,031.83	$1,031.90	$1,031.90