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	$126.28	11.294%	$140.5421	$140.54	$140.55	$140.50
Purchase #2	$77.77	3.424%	$80.4328	$80.43	$80.45	$80.40
Purchase #3	$235.35	8.516%	$255.3924	$255.39	$255.40	$255.40
Purchase #4	$153.42	12.453%	$172.5254	$172.53	$172.55	$172.50
Purchase #5	$44.54	13.574%	$50.5859	$50.59	$50.60	$50.60
Purchase #6	$79.29	4.538%	$82.8882	$82.89	$82.90	$82.90
Purchase #7	$70.58	13.463%	$80.0822	$80.08	$80.10	$80.10
7 purchase totals =	$787.23		$862.4490	$862.45	$862.55	$862.40