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	$39.46	7.681%	$42.4909	$42.49	$42.50	$42.50
Purchase #2	$28.77	10.680%	$31.8426	$31.84	$31.85	$31.80
Purchase #3	$119.48	7.255%	$128.1483	$128.15	$128.15	$128.10
Purchase #4	$60.90	4.228%	$63.4749	$63.47	$63.45	$63.50
Purchase #5	$124.52	13.366%	$141.1633	$141.16	$141.15	$141.20
Purchase #6	$31.62	4.152%	$32.9329	$32.93	$32.95	$32.90
Purchase #7	$132.34	4.813%	$138.7095	$138.71	$138.70	$138.70
7 purchase totals =	$537.09		$578.7624	$578.75	$578.75	$578.70