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	$35.52	5.492%	$37.4708	$37.47	$37.45	$37.50
Purchase #2	$240.75	9.537%	$263.7103	$263.71	$263.70	$263.70
Purchase #3	$44.41	13.161%	$50.2548	$50.25	$50.25	$50.30
Purchase #4	$241.69	7.472%	$259.7491	$259.75	$259.75	$259.70
Purchase #5	$37.54	8.104%	$40.5822	$40.58	$40.60	$40.60
Purchase #6	$45.82	11.656%	$51.1608	$51.16	$51.15	$51.20
Purchase #7	$184.81	13.455%	$209.6762	$209.68	$209.70	$209.70
7 purchase totals =	$830.54		$912.6042	$912.60	$912.60	$912.70