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	$61.25	11.271%	$68.1535	$68.15	$68.15	$68.20
Purchase #2	$56.51	5.643%	$59.6989	$59.70	$59.70	$59.70
Purchase #3	$216.77	10.675%	$239.9102	$239.91	$239.90	$239.90
Purchase #4	$61.46	11.202%	$68.3447	$68.34	$68.35	$68.30
Purchase #5	$229.95	12.278%	$258.1833	$258.18	$258.20	$258.20
Purchase #6	$81.27	11.332%	$90.4795	$90.48	$90.50	$90.50
Purchase #7	$49.61	10.757%	$54.9465	$54.95	$54.95	$54.90
7 purchase totals =	$756.82		$839.7166	$839.71	$839.75	$839.70