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	$199.71	10.354%	$220.388	$220.39	$220.40	$220.40
Purchase #2	$39.27	7.421%	$42.1842	$42.18	$42.20	$42.20
Purchase #3	$68.49	11.783%	$76.5602	$76.56	$76.55	$76.60
Purchase #4	$143.77	3.314%	$148.5345	$148.53	$148.55	$148.50
Purchase #5	$46.86	10.851%	$51.9448	$51.94	$51.95	$51.90
Purchase #6	$29.27	8.604%	$31.7884	$31.79	$31.80	$31.80
Purchase #7	$77.46	6.606%	$82.577	$82.58	$82.60	$82.60
7 purchase totals =	$604.83		$653.9771	$653.97	$654.05	$654.00