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	$49.75	13.426%	$56.4294	$56.43	$56.45	$56.40
Purchase #2	$130.36	7.484%	$140.1161	$140.12	$140.10	$140.10
Purchase #3	$9.46	11.715%	$10.5682	$10.57	$10.55	$10.60
Purchase #4	$18.72	6.182%	$19.8773	$19.88	$19.90	$19.90
Purchase #5	$12.46	3.163%	$12.8541	$12.85	$12.85	$12.90
Purchase #6	$50.67	5.703%	$53.5597	$53.56	$53.55	$53.60
Purchase #7	$175.35	5.781%	$185.487	$185.49	$185.50	$185.50
7 purchase totals =	$446.77		$478.8918	$478.90	$478.90	$479.00