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	$241.54	12.358%	$271.3895	$271.39	$271.40	$271.40
Purchase #2	$92.52	7.110%	$99.0982	$99.10	$99.10	$99.10
Purchase #3	$24.97	8.841%	$27.1776	$27.18	$27.20	$27.20
Purchase #4	$73.70	12.835%	$83.1594	$83.16	$83.15	$83.20
Purchase #5	$104.49	6.308%	$111.0812	$111.08	$111.10	$111.10
Purchase #6	$17.69	3.531%	$18.3146	$18.31	$18.30	$18.30
Purchase #7	$30.50	8.395%	$33.0605	$33.06	$33.05	$33.10
7 purchase totals =	$585.41		$643.2810	$643.28	$643.30	$643.40