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	$11.58	6.823%	$12.3701	$12.37	$12.35	$12.40
Purchase #2	$187.67	12.555%	$211.232	$211.23	$211.25	$211.20
Purchase #3	$83.85	6.689%	$89.4587	$89.46	$89.45	$89.50
Purchase #4	$38.52	11.765%	$43.0519	$43.05	$43.05	$43.10
Purchase #5	$23.69	5.338%	$24.9546	$24.95	$24.95	$25.00
Purchase #6	$28.43	4.198%	$29.6235	$29.62	$29.60	$29.60
Purchase #7	$244.85	11.421%	$272.8143	$272.81	$272.80	$272.80
7 purchase totals =	$618.59		$683.5051	$683.49	$683.45	$683.60