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	$144.88	10.836%	$160.5792	$160.58	$160.60	$160.60
Purchase #2	$82.66	8.353%	$89.5646	$89.56	$89.55	$89.60
Purchase #3	$82.58	8.178%	$89.3334	$89.33	$89.35	$89.30
Purchase #4	$146.98	9.755%	$161.3179	$161.32	$161.30	$161.30
Purchase #5	$249.33	12.402%	$280.2519	$280.25	$280.25	$280.30
Purchase #6	$235.49	8.452%	$255.3936	$255.39	$255.40	$255.40
Purchase #7	$39.44	6.500%	$42.0036	$42.00	$42.00	$42.00
7 purchase totals =	$981.36		$1,078.4442	$1,078.43	$1,078.45	$1,078.50