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	$12.65	7.343%	$13.5789	$13.58	$13.60	$13.60
Purchase #2	$172.51	3.661%	$178.8256	$178.83	$178.85	$178.80
Purchase #3	$18.46	12.620%	$20.7897	$20.79	$20.80	$20.80
Purchase #4	$113.28	10.163%	$124.7926	$124.79	$124.80	$124.80
Purchase #5	$236.62	8.327%	$256.3233	$256.32	$256.30	$256.30
Purchase #6	$221.74	4.456%	$231.6207	$231.62	$231.60	$231.60
Purchase #7	$100.31	12.177%	$112.5247	$112.52	$112.50	$112.50
7 purchase totals =	$875.57		$938.4555	$938.45	$938.45	$938.40