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	$242.52	8.770%	$263.789	$263.79	$263.80	$263.80
Purchase #2	$32.65	4.204%	$34.0226	$34.02	$34.00	$34.00
Purchase #3	$20.53	5.247%	$21.6072	$21.61	$21.60	$21.60
Purchase #4	$221.54	4.213%	$230.8735	$230.87	$230.85	$230.90
Purchase #5	$89.51	10.406%	$98.8244	$98.82	$98.80	$98.80
Purchase #6	$75.94	9.723%	$83.3236	$83.32	$83.30	$83.30
Purchase #7	$128.96	5.813%	$136.4564	$136.46	$136.45	$136.50
7 purchase totals =	$811.65		$868.8967	$868.89	$868.80	$868.90