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	$20.56	6.531%	$21.9028	$21.90	$21.90	$21.90
Purchase #2	$108.28	3.374%	$111.9334	$111.93	$111.95	$111.90
Purchase #3	$49.51	13.765%	$56.3251	$56.33	$56.35	$56.30
Purchase #4	$45.95	4.527%	$48.0302	$48.03	$48.05	$48.00
Purchase #5	$121.48	13.248%	$137.5737	$137.57	$137.55	$137.60
Purchase #6	$132.28	10.783%	$146.5438	$146.54	$146.55	$146.50
Purchase #7	$214.95	13.785%	$244.5809	$244.58	$244.60	$244.60
7 purchase totals =	$693.01		$766.8899	$766.88	$766.95	$766.80