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	$152.86	13.700%	$173.8018	$173.80	$173.80	$173.80
Purchase #2	$60.52	4.619%	$63.3154	$63.32	$63.30	$63.30
Purchase #3	$128.40	11.476%	$143.1352	$143.14	$143.15	$143.10
Purchase #4	$30.42	10.495%	$33.6126	$33.61	$33.60	$33.60
Purchase #5	$38.96	3.813%	$40.4455	$40.45	$40.45	$40.40
Purchase #6	$231.80	7.629%	$249.484	$249.48	$249.50	$249.50
Purchase #7	$54.97	9.794%	$60.3538	$60.35	$60.35	$60.40
7 purchase totals =	$697.93		$764.1483	$764.15	$764.15	$764.10