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	$38.90	9.314%	$42.5231	$42.52	$42.50	$42.50
Purchase #2	$19.36	3.173%	$19.9743	$19.97	$19.95	$20.00
Purchase #3	$133.29	7.225%	$142.9202	$142.92	$142.90	$142.90
Purchase #4	$90.73	12.827%	$102.3679	$102.37	$102.35	$102.40
Purchase #5	$178.89	11.198%	$198.9221	$198.92	$198.90	$198.90
Purchase #6	$150.45	5.301%	$158.4254	$158.43	$158.45	$158.40
Purchase #7	$15.79	10.348%	$17.4239	$17.42	$17.40	$17.40
7 purchase totals =	$627.41		$682.5569	$682.55	$682.45	$682.50