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	$240.72	5.462%	$253.8681	$253.87	$253.85	$253.90
Purchase #2	$151.52	4.229%	$157.9278	$157.93	$157.95	$157.90
Purchase #3	$18.55	10.811%	$20.5554	$20.56	$20.55	$20.60
Purchase #4	$59.57	3.262%	$61.5132	$61.51	$61.50	$61.50
Purchase #5	$7.50	12.676%	$8.4507	$8.45	$8.45	$8.50
Purchase #6	$20.49	5.429%	$21.6024	$21.60	$21.60	$21.60
Purchase #7	$135.38	4.368%	$141.2934	$141.29	$141.30	$141.30
7 purchase totals =	$633.73		$665.2110	$665.21	$665.20	$665.30