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	$245.59	8.717%	$266.9981	$267.00	$267.00	$267.00
Purchase #2	$70.72	13.648%	$80.3719	$80.37	$80.35	$80.40
Purchase #3	$145.52	7.348%	$156.2128	$156.21	$156.20	$156.20
Purchase #4	$159.82	12.359%	$179.5722	$179.57	$179.55	$179.60
Purchase #5	$75.58	10.401%	$83.4411	$83.44	$83.45	$83.40
Purchase #6	$159.69	13.723%	$181.6043	$181.60	$181.60	$181.60
Purchase #7	$48.55	4.745%	$50.8537	$50.85	$50.85	$50.90
7 purchase totals =	$905.47		$999.0541	$999.04	$999.00	$999.10