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	$25.64	7.518%	$27.5676	$27.57	$27.55	$27.60
Purchase #2	$133.58	13.382%	$151.4557	$151.46	$151.45	$151.50
Purchase #3	$232.34	9.445%	$254.2845	$254.28	$254.30	$254.30
Purchase #4	$26.51	4.360%	$27.6658	$27.67	$27.65	$27.70
Purchase #5	$56.51	5.397%	$59.5598	$59.56	$59.55	$59.60
Purchase #6	$142.37	10.570%	$157.4185	$157.42	$157.40	$157.40
Purchase #7	$138.73	4.327%	$144.7328	$144.73	$144.75	$144.70
7 purchase totals =	$755.68		$822.6847	$822.69	$822.65	$822.80