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	$33.28	10.837%	$36.8866	$36.89	$36.90	$36.90
Purchase #2	$65.37	11.538%	$72.9124	$72.91	$72.90	$72.90
Purchase #3	$200.27	10.416%	$221.1301	$221.13	$221.15	$221.10
Purchase #4	$69.86	4.262%	$72.8374	$72.84	$72.85	$72.80
Purchase #5	$151.72	11.756%	$169.5562	$169.56	$169.55	$169.60
Purchase #6	$208.54	8.472%	$226.2075	$226.21	$226.20	$226.20
Purchase #7	$123.86	5.400%	$130.5484	$130.55	$130.55	$130.50
7 purchase totals =	$852.90		$930.0786	$930.09	$930.10	$930.00