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	$95.81	3.770%	$99.422	$99.42	$99.40	$99.40
Purchase #2	$144.96	6.541%	$154.4418	$154.44	$154.45	$154.40
Purchase #3	$223.57	7.340%	$239.98	$239.98	$240.00	$240.00
Purchase #4	$69.25	4.660%	$72.4771	$72.48	$72.50	$72.50
Purchase #5	$111.76	4.623%	$116.9267	$116.93	$116.95	$116.90
Purchase #6	$38.94	13.502%	$44.1977	$44.20	$44.20	$44.20
Purchase #7	$133.59	7.585%	$143.7228	$143.72	$143.70	$143.70
7 purchase totals =	$817.88		$871.1681	$871.17	$871.20	$871.10