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	$22.30	10.156%	$24.5648	$24.56	$24.55	$24.60
Purchase #2	$72.84	13.494%	$82.669	$82.67	$82.65	$82.70
Purchase #3	$143.29	8.174%	$155.0025	$155.00	$155.00	$155.00
Purchase #4	$13.84	12.170%	$15.5243	$15.52	$15.50	$15.50
Purchase #5	$147.79	4.585%	$154.5662	$154.57	$154.55	$154.60
Purchase #6	$75.79	3.856%	$78.7125	$78.71	$78.70	$78.70
Purchase #7	$96.86	4.845%	$101.5529	$101.55	$101.55	$101.60
7 purchase totals =	$572.71		$612.5922	$612.58	$612.50	$612.70