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	$196.95	13.520%	$223.5776	$223.58	$223.60	$223.60
Purchase #2	$90.78	13.674%	$103.1933	$103.19	$103.20	$103.20
Purchase #3	$206.34	10.865%	$228.7588	$228.76	$228.75	$228.80
Purchase #4	$111.29	7.372%	$119.4943	$119.49	$119.50	$119.50
Purchase #5	$14.45	3.777%	$14.9958	$15.00	$15.00	$15.00
Purchase #6	$139.75	5.823%	$147.8876	$147.89	$147.90	$147.90
Purchase #7	$108.94	3.864%	$113.1494	$113.15	$113.15	$113.10
7 purchase totals =	$868.50		$951.0568	$951.06	$951.10	$951.10