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	12.252%	$12.3365	$12.34	$12.35	$12.30
Purchase #2	$43.86	4.756%	$45.946	$45.95	$45.95	$45.90
Purchase #3	$17.56	10.119%	$19.3369	$19.34	$19.35	$19.30
Purchase #4	$111.79	10.777%	$123.8376	$123.84	$123.85	$123.80
Purchase #5	$72.35	11.382%	$80.5849	$80.58	$80.60	$80.60
Purchase #6	$214.48	11.285%	$238.6841	$238.68	$238.70	$238.70
Purchase #7	$109.28	9.791%	$119.9796	$119.98	$120.00	$120.00
7 purchase totals =	$580.31		$640.7056	$640.71	$640.80	$640.60