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	$19.70	8.376%	$21.3501	$21.35	$21.35	$21.40
Purchase #2	$101.40	7.329%	$108.8316	$108.83	$108.85	$108.80
Purchase #3	$60.97	10.572%	$67.4157	$67.42	$67.40	$67.40
Purchase #4	$54.67	5.274%	$57.5533	$57.55	$57.55	$57.60
Purchase #5	$248.57	11.695%	$277.6403	$277.64	$277.65	$277.60
Purchase #6	$60.89	10.444%	$67.2494	$67.25	$67.25	$67.20
Purchase #7	$68.84	5.509%	$72.6324	$72.63	$72.65	$72.60
7 purchase totals =	$615.04		$672.6728	$672.67	$672.70	$672.60