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	$45.29	4.249%	$47.2144	$47.21	$47.20	$47.20
Purchase #2	$69.95	9.772%	$76.7855	$76.79	$76.80	$76.80
Purchase #3	$76.30	3.140%	$78.6958	$78.70	$78.70	$78.70
Purchase #4	$150.93	6.676%	$161.0061	$161.01	$161.00	$161.00
Purchase #5	$138.95	10.860%	$154.04	$154.04	$154.05	$154.00
Purchase #6	$79.33	12.380%	$89.1511	$89.15	$89.15	$89.20
Purchase #7	$38.60	13.527%	$43.8214	$43.82	$43.80	$43.80
7 purchase totals =	$599.35		$650.7143	$650.72	$650.70	$650.70