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	$38.49	9.751%	$42.2432	$42.24	$42.25	$42.20
Purchase #2	$10.68	13.737%	$12.1471	$12.15	$12.15	$12.10
Purchase #3	$182.76	12.248%	$205.1444	$205.14	$205.15	$205.10
Purchase #4	$240.56	11.245%	$267.611	$267.61	$267.60	$267.60
Purchase #5	$42.45	4.580%	$44.3942	$44.39	$44.40	$44.40
Purchase #6	$103.81	4.509%	$108.4908	$108.49	$108.50	$108.50
Purchase #7	$161.56	12.676%	$182.0393	$182.04	$182.05	$182.00
7 purchase totals =	$780.31		$862.0700	$862.06	$862.10	$861.90