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	$34.92	9.695%	$38.3055	$38.31	$38.30	$38.30
Purchase #2	$145.27	7.126%	$155.6219	$155.62	$155.60	$155.60
Purchase #3	$173.91	11.839%	$194.4992	$194.50	$194.50	$194.50
Purchase #4	$144.70	8.205%	$156.5726	$156.57	$156.55	$156.60
Purchase #5	$9.81	3.556%	$10.1588	$10.16	$10.15	$10.20
Purchase #6	$144.92	13.679%	$164.7436	$164.74	$164.75	$164.70
Purchase #7	$20.45	5.401%	$21.5545	$21.55	$21.55	$21.60
7 purchase totals =	$673.98		$741.4561	$741.45	$741.40	$741.50