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	$248.87	8.340%	$269.6258	$269.63	$269.65	$269.60
Purchase #2	$132.77	6.686%	$141.647	$141.65	$141.65	$141.60
Purchase #3	$169.46	13.557%	$192.4337	$192.43	$192.45	$192.40
Purchase #4	$126.85	5.379%	$133.6733	$133.67	$133.65	$133.70
Purchase #5	$130.81	10.771%	$144.8995	$144.90	$144.90	$144.90
Purchase #6	$222.67	4.856%	$233.4829	$233.48	$233.50	$233.50
Purchase #7	$100.83	4.412%	$105.2786	$105.28	$105.30	$105.30
7 purchase totals =	$1,132.26		$1,221.0408	$1,221.04	$1,221.10	$1,221.00