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	$91.58	13.102%	$103.5788	$103.58	$103.60	$103.60
Purchase #2	$126.85	13.341%	$143.7731	$143.77	$143.75	$143.80
Purchase #3	$123.93	3.491%	$128.2564	$128.26	$128.25	$128.30
Purchase #4	$48.62	10.275%	$53.6157	$53.62	$53.60	$53.60
Purchase #5	$41.42	3.526%	$42.8805	$42.88	$42.90	$42.90
Purchase #6	$244.40	12.434%	$274.7887	$274.79	$274.80	$274.80
Purchase #7	$241.61	5.857%	$255.7611	$255.76	$255.75	$255.80
7 purchase totals =	$918.41		$1,002.6543	$1,002.66	$1,002.65	$1,002.80