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	$18.32	6.678%	$19.5434	$19.54	$19.55	$19.50
Purchase #2	$229.91	13.514%	$260.98	$260.98	$261.00	$261.00
Purchase #3	$11.44	5.205%	$12.0355	$12.04	$12.05	$12.00
Purchase #4	$48.91	12.336%	$54.9435	$54.94	$54.95	$54.90
Purchase #5	$94.77	11.784%	$105.9377	$105.94	$105.95	$105.90
Purchase #6	$50.47	13.712%	$57.3904	$57.39	$57.40	$57.40
Purchase #7	$71.80	12.426%	$80.7219	$80.72	$80.70	$80.70
7 purchase totals =	$525.62		$591.5524	$591.55	$591.60	$591.40