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	$65.64	3.259%	$67.7792	$67.78	$67.80	$67.80
Purchase #2	$144.78	4.763%	$151.6759	$151.68	$151.70	$151.70
Purchase #3	$219.96	6.150%	$233.4875	$233.49	$233.50	$233.50
Purchase #4	$76.50	5.563%	$80.7557	$80.76	$80.75	$80.80
Purchase #5	$42.40	4.424%	$44.2758	$44.28	$44.30	$44.30
Purchase #6	$11.86	10.749%	$13.1348	$13.13	$13.15	$13.10
Purchase #7	$87.76	3.264%	$90.6245	$90.62	$90.60	$90.60
7 purchase totals =	$648.90		$681.7334	$681.74	$681.80	$681.80