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	$228.99	12.728%	$258.1358	$258.14	$258.15	$258.10
Purchase #2	$19.47	4.846%	$20.4135	$20.41	$20.40	$20.40
Purchase #3	$21.30	13.510%	$24.1776	$24.18	$24.20	$24.20
Purchase #4	$28.39	13.772%	$32.2999	$32.30	$32.30	$32.30
Purchase #5	$46.51	12.610%	$52.3749	$52.37	$52.35	$52.40
Purchase #6	$144.61	11.761%	$161.6176	$161.62	$161.60	$161.60
Purchase #7	$127.51	12.554%	$143.5176	$143.52	$143.50	$143.50
7 purchase totals =	$616.78		$692.5369	$692.54	$692.50	$692.50