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	$113.36	5.103%	$119.1448	$119.14	$119.15	$119.10
Purchase #2	$85.40	10.702%	$94.5395	$94.54	$94.55	$94.50
Purchase #3	$145.50	8.675%	$158.1221	$158.12	$158.10	$158.10
Purchase #4	$225.52	13.761%	$256.5538	$256.55	$256.55	$256.60
Purchase #5	$32.54	5.758%	$34.4137	$34.41	$34.40	$34.40
Purchase #6	$109.32	5.119%	$114.9161	$114.92	$114.90	$114.90
Purchase #7	$53.59	4.436%	$55.9673	$55.97	$55.95	$56.00
7 purchase totals =	$765.23		$833.6573	$833.65	$833.60	$833.60