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	$28.48	13.621%	$32.3593	$32.36	$32.35	$32.40
Purchase #2	$66.37	3.530%	$68.7129	$68.71	$68.70	$68.70
Purchase #3	$220.71	8.231%	$238.8766	$238.88	$238.90	$238.90
Purchase #4	$96.40	4.128%	$100.3794	$100.38	$100.40	$100.40
Purchase #5	$9.71	7.340%	$10.4227	$10.42	$10.40	$10.40
Purchase #6	$37.39	3.240%	$38.6014	$38.60	$38.60	$38.60
Purchase #7	$92.39	4.873%	$96.8922	$96.89	$96.90	$96.90
7 purchase totals =	$551.45		$586.2445	$586.24	$586.25	$586.30