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	$221.66	9.553%	$242.8352	$242.84	$242.85	$242.80
Purchase #2	$206.46	8.553%	$224.1185	$224.12	$224.10	$224.10
Purchase #3	$103.68	8.852%	$112.8578	$112.86	$112.85	$112.90
Purchase #4	$86.82	3.494%	$89.8535	$89.85	$89.85	$89.90
Purchase #5	$69.70	12.606%	$78.4864	$78.49	$78.50	$78.50
Purchase #6	$34.76	13.467%	$39.4411	$39.44	$39.45	$39.40
Purchase #7	$142.95	3.180%	$147.4958	$147.50	$147.50	$147.50
7 purchase totals =	$866.03		$935.0883	$935.10	$935.10	$935.10