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	$81.76	10.510%	$90.353	$90.35	$90.35	$90.40
Purchase #2	$214.78	7.495%	$230.8778	$230.88	$230.90	$230.90
Purchase #3	$44.29	5.137%	$46.5652	$46.57	$46.55	$46.60
Purchase #4	$72.28	13.470%	$82.0161	$82.02	$82.00	$82.00
Purchase #5	$6.80	8.247%	$7.3608	$7.36	$7.35	$7.40
Purchase #6	$15.66	6.139%	$16.6214	$16.62	$16.60	$16.60
Purchase #7	$56.93	13.762%	$64.7647	$64.76	$64.75	$64.80
7 purchase totals =	$492.50		$538.5590	$538.56	$538.50	$538.70