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	$35.39	13.837%	$40.2869	$40.29	$40.30	$40.30
Purchase #2	$48.34	10.689%	$53.5071	$53.51	$53.50	$53.50
Purchase #3	$24.87	10.621%	$27.5114	$27.51	$27.50	$27.50
Purchase #4	$143.26	5.841%	$151.6278	$151.63	$151.65	$151.60
Purchase #5	$229.86	12.873%	$259.4499	$259.45	$259.45	$259.40
Purchase #6	$68.81	4.659%	$72.0159	$72.02	$72.00	$72.00
Purchase #7	$191.98	6.806%	$205.0462	$205.05	$205.05	$205.00
7 purchase totals =	$742.51		$809.4452	$809.46	$809.45	$809.30