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	$72.69	13.805%	$82.7249	$82.72	$82.70	$82.70
Purchase #2	$49.42	12.659%	$55.6761	$55.68	$55.70	$55.70
Purchase #3	$168.55	4.778%	$176.6033	$176.60	$176.60	$176.60
Purchase #4	$146.28	5.533%	$154.3737	$154.37	$154.35	$154.40
Purchase #5	$148.32	9.232%	$162.0129	$162.01	$162.00	$162.00
Purchase #6	$128.35	10.751%	$142.1489	$142.15	$142.15	$142.10
Purchase #7	$42.37	12.247%	$47.5591	$47.56	$47.55	$47.60
7 purchase totals =	$755.98		$821.0989	$821.09	$821.05	$821.10