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	$213.42	12.788%	$240.7121	$240.71	$240.70	$240.70
Purchase #2	$118.48	13.761%	$134.784	$134.78	$134.80	$134.80
Purchase #3	$49.73	3.714%	$51.577	$51.58	$51.60	$51.60
Purchase #4	$78.95	10.592%	$87.3124	$87.31	$87.30	$87.30
Purchase #5	$82.81	9.649%	$90.8003	$90.80	$90.80	$90.80
Purchase #6	$81.85	4.210%	$85.2959	$85.30	$85.30	$85.30
Purchase #7	$175.39	8.419%	$190.1561	$190.16	$190.15	$190.20
7 purchase totals =	$800.63		$880.6378	$880.64	$880.65	$880.70