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	$51.89	13.746%	$59.0228	$59.02	$59.00	$59.00
Purchase #2	$36.81	7.629%	$39.6182	$39.62	$39.60	$39.60
Purchase #3	$204.28	9.389%	$223.4598	$223.46	$223.45	$223.50
Purchase #4	$19.51	4.750%	$20.4367	$20.44	$20.45	$20.40
Purchase #5	$154.54	9.504%	$169.2275	$169.23	$169.25	$169.20
Purchase #6	$13.42	3.208%	$13.8505	$13.85	$13.85	$13.90
Purchase #7	$223.67	13.189%	$253.1698	$253.17	$253.15	$253.20
7 purchase totals =	$704.12		$778.7853	$778.79	$778.75	$778.80