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	$62.37	13.387%	$70.7195	$70.72	$70.70	$70.70
Purchase #2	$177.80	12.584%	$200.1744	$200.17	$200.15	$200.20
Purchase #3	$117.72	4.638%	$123.1799	$123.18	$123.20	$123.20
Purchase #4	$158.45	9.385%	$173.3205	$173.32	$173.30	$173.30
Purchase #5	$202.55	9.327%	$221.4418	$221.44	$221.45	$221.40
Purchase #6	$11.77	9.406%	$12.8771	$12.88	$12.90	$12.90
Purchase #7	$93.95	4.736%	$98.3995	$98.40	$98.40	$98.40
7 purchase totals =	$824.61		$900.1127	$900.11	$900.10	$900.10