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	$182.72	9.802%	$200.6302	$200.63	$200.65	$200.60
Purchase #2	$93.79	11.253%	$104.3442	$104.34	$104.35	$104.30
Purchase #3	$224.65	7.177%	$240.7731	$240.77	$240.75	$240.80
Purchase #4	$9.80	11.145%	$10.8922	$10.89	$10.90	$10.90
Purchase #5	$123.81	13.444%	$140.455	$140.46	$140.45	$140.50
Purchase #6	$10.43	3.569%	$10.8022	$10.80	$10.80	$10.80
Purchase #7	$82.87	9.355%	$90.6225	$90.62	$90.60	$90.60
7 purchase totals =	$728.07		$798.5194	$798.51	$798.50	$798.50