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	$10.99	8.418%	$11.9151	$11.92	$11.90	$11.90
Purchase #2	$144.32	4.691%	$151.0901	$151.09	$151.10	$151.10
Purchase #3	$18.45	11.470%	$20.5662	$20.57	$20.55	$20.60
Purchase #4	$215.52	6.700%	$229.9598	$229.96	$229.95	$230.00
Purchase #5	$46.59	10.656%	$51.5546	$51.55	$51.55	$51.60
Purchase #6	$112.25	13.462%	$127.3611	$127.36	$127.35	$127.40
Purchase #7	$84.30	5.512%	$88.9466	$88.95	$88.95	$88.90
7 purchase totals =	$632.42		$681.3935	$681.40	$681.35	$681.50