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	$84.66	6.607%	$90.2535	$90.25	$90.25	$90.30
Purchase #2	$179.78	8.682%	$195.3885	$195.39	$195.40	$195.40
Purchase #3	$168.47	4.145%	$175.4531	$175.45	$175.45	$175.50
Purchase #4	$154.52	13.631%	$175.5826	$175.58	$175.60	$175.60
Purchase #5	$141.78	9.225%	$154.8592	$154.86	$154.85	$154.90
Purchase #6	$109.60	6.324%	$116.5311	$116.53	$116.55	$116.50
Purchase #7	$48.76	6.207%	$51.7865	$51.79	$51.80	$51.80
7 purchase totals =	$887.57		$959.8545	$959.85	$959.90	$960.00