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	$32.40	3.644%	$33.5807	$33.58	$33.60	$33.60
Purchase #2	$87.25	13.599%	$99.1151	$99.12	$99.10	$99.10
Purchase #3	$170.61	11.668%	$190.5168	$190.52	$190.50	$190.50
Purchase #4	$116.59	4.836%	$122.2283	$122.23	$122.25	$122.20
Purchase #5	$248.46	5.662%	$262.5278	$262.53	$262.55	$262.50
Purchase #6	$75.57	12.676%	$85.1493	$85.15	$85.15	$85.10
Purchase #7	$74.26	10.310%	$81.9162	$81.92	$81.90	$81.90
7 purchase totals =	$805.14		$875.0342	$875.05	$875.05	$874.90