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	$21.60	10.855%	$23.9447	$23.94	$23.95	$23.90
Purchase #2	$101.84	9.632%	$111.6492	$111.65	$111.65	$111.60
Purchase #3	$79.47	13.131%	$89.9052	$89.91	$89.90	$89.90
Purchase #4	$49.58	12.498%	$55.7765	$55.78	$55.80	$55.80
Purchase #5	$208.64	11.473%	$232.5773	$232.58	$232.60	$232.60
Purchase #6	$184.56	3.301%	$190.6523	$190.65	$190.65	$190.70
Purchase #7	$26.57	4.523%	$27.7718	$27.77	$27.75	$27.80
7 purchase totals =	$672.26		$732.2770	$732.28	$732.30	$732.30