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	$104.31	11.771%	$116.5883	$116.59	$116.60	$116.60
Purchase #2	$80.78	8.727%	$87.8297	$87.83	$87.85	$87.80
Purchase #3	$196.56	10.631%	$217.4563	$217.46	$217.45	$217.50
Purchase #4	$165.71	5.285%	$174.4678	$174.47	$174.45	$174.50
Purchase #5	$96.77	3.497%	$100.154	$100.15	$100.15	$100.20
Purchase #6	$142.25	5.487%	$150.0553	$150.06	$150.05	$150.10
Purchase #7	$82.72	10.868%	$91.71	$91.71	$91.70	$91.70
7 purchase totals =	$869.10		$938.2614	$938.27	$938.25	$938.40