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	$248.92	5.528%	$262.6803	$262.68	$262.70	$262.70
Purchase #2	$117.49	12.238%	$131.8684	$131.87	$131.85	$131.90
Purchase #3	$11.85	6.619%	$12.6344	$12.63	$12.65	$12.60
Purchase #4	$20.78	4.116%	$21.6353	$21.64	$21.65	$21.60
Purchase #5	$162.33	3.444%	$167.9206	$167.92	$167.90	$167.90
Purchase #6	$238.34	11.532%	$265.8254	$265.83	$265.85	$265.80
Purchase #7	$99.41	12.821%	$112.1554	$112.16	$112.15	$112.20
7 purchase totals =	$899.12		$974.7198	$974.73	$974.75	$974.70