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	$39.65	7.702%	$42.7038	$42.70	$42.70	$42.70
Purchase #2	$212.75	9.731%	$233.4527	$233.45	$233.45	$233.50
Purchase #3	$224.80	12.419%	$252.7179	$252.72	$252.70	$252.70
Purchase #4	$115.80	3.287%	$119.6063	$119.61	$119.60	$119.60
Purchase #5	$122.27	13.809%	$139.1543	$139.15	$139.15	$139.20
Purchase #6	$234.88	8.861%	$255.6927	$255.69	$255.70	$255.70
Purchase #7	$116.62	10.133%	$128.4371	$128.44	$128.45	$128.40
7 purchase totals =	$1,066.77		$1,171.7648	$1,171.76	$1,171.75	$1,171.80