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	$19.95	4.692%	$20.8861	$20.89	$20.90	$20.90
Purchase #2	$156.96	7.547%	$168.8058	$168.81	$168.80	$168.80
Purchase #3	$137.97	4.136%	$143.6764	$143.68	$143.70	$143.70
Purchase #4	$67.45	6.223%	$71.6474	$71.65	$71.65	$71.60
Purchase #5	$152.50	12.785%	$171.9971	$172.00	$172.00	$172.00
Purchase #6	$49.89	4.635%	$52.2024	$52.20	$52.20	$52.20
Purchase #7	$89.43	6.618%	$95.3485	$95.35	$95.35	$95.30
7 purchase totals =	$674.15		$724.5637	$724.58	$724.60	$724.50