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	$80.79	6.787%	$86.2732	$86.27	$86.25	$86.30
Purchase #2	$214.87	3.598%	$222.601	$222.60	$222.60	$222.60
Purchase #3	$105.48	13.792%	$120.0278	$120.03	$120.05	$120.00
Purchase #4	$117.89	5.789%	$124.7147	$124.71	$124.70	$124.70
Purchase #5	$111.27	4.714%	$116.5153	$116.52	$116.50	$116.50
Purchase #6	$44.61	7.150%	$47.7996	$47.80	$47.80	$47.80
Purchase #7	$164.85	5.131%	$173.3085	$173.31	$173.30	$173.30
7 purchase totals =	$839.76		$891.2401	$891.24	$891.20	$891.20