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	$18.31	11.475%	$20.4111	$20.41	$20.40	$20.40
Purchase #2	$49.56	5.670%	$52.3701	$52.37	$52.35	$52.40
Purchase #3	$54.74	10.488%	$60.4811	$60.48	$60.50	$60.50
Purchase #4	$35.27	4.510%	$36.8607	$36.86	$36.85	$36.90
Purchase #5	$244.60	4.463%	$255.5165	$255.52	$255.50	$255.50
Purchase #6	$213.37	12.333%	$239.6849	$239.68	$239.70	$239.70
Purchase #7	$50.96	10.665%	$56.3949	$56.39	$56.40	$56.40
7 purchase totals =	$666.81		$721.7193	$721.71	$721.70	$721.80