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	$40.86	4.289%	$42.6125	$42.61	$42.60	$42.60
Purchase #2	$145.45	9.152%	$158.7616	$158.76	$158.75	$158.80
Purchase #3	$59.97	5.265%	$63.1274	$63.13	$63.15	$63.10
Purchase #4	$182.64	9.563%	$200.1059	$200.11	$200.10	$200.10
Purchase #5	$183.78	3.543%	$190.2913	$190.29	$190.30	$190.30
Purchase #6	$163.54	3.345%	$169.0104	$169.01	$169.00	$169.00
Purchase #7	$246.78	13.701%	$280.5913	$280.59	$280.60	$280.60
7 purchase totals =	$1,023.02		$1,104.5004	$1,104.50	$1,104.50	$1,104.50