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	$246.46	13.804%	$280.4813	$280.48	$280.50	$280.50
Purchase #2	$57.80	13.834%	$65.7961	$65.80	$65.80	$65.80
Purchase #3	$207.96	7.782%	$224.1434	$224.14	$224.15	$224.10
Purchase #4	$131.63	12.757%	$148.422	$148.42	$148.40	$148.40
Purchase #5	$93.71	9.381%	$102.5009	$102.50	$102.50	$102.50
Purchase #6	$187.72	9.327%	$205.2286	$205.23	$205.25	$205.20
Purchase #7	$110.38	12.688%	$124.385	$124.39	$124.40	$124.40
7 purchase totals =	$1,035.66		$1,150.9573	$1,150.96	$1,151.00	$1,150.90