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	$133.92	13.128%	$151.501	$151.50	$151.50	$151.50
Purchase #2	$29.29	10.235%	$32.2878	$32.29	$32.30	$32.30
Purchase #3	$143.27	3.388%	$148.124	$148.12	$148.10	$148.10
Purchase #4	$49.93	9.704%	$54.7752	$54.78	$54.80	$54.80
Purchase #5	$124.58	11.631%	$139.0699	$139.07	$139.05	$139.10
Purchase #6	$53.45	4.615%	$55.9167	$55.92	$55.90	$55.90
Purchase #7	$134.28	5.615%	$141.8198	$141.82	$141.80	$141.80
7 purchase totals =	$668.72		$723.4944	$723.50	$723.45	$723.50