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	$179.25	5.741%	$189.5407	$189.54	$189.55	$189.50
Purchase #2	$60.80	10.161%	$66.9779	$66.98	$67.00	$67.00
Purchase #3	$50.82	10.220%	$56.0138	$56.01	$56.00	$56.00
Purchase #4	$196.47	4.762%	$205.8259	$205.83	$205.85	$205.80
Purchase #5	$211.91	7.625%	$228.0681	$228.07	$228.05	$228.10
Purchase #6	$58.82	13.477%	$66.7472	$66.75	$66.75	$66.70
Purchase #7	$28.75	9.278%	$31.4174	$31.42	$31.40	$31.40
7 purchase totals =	$786.82		$844.5910	$844.60	$844.60	$844.50