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	$135.48	4.468%	$141.5332	$141.53	$141.55	$141.50
Purchase #2	$126.85	13.828%	$144.3908	$144.39	$144.40	$144.40
Purchase #3	$185.65	10.868%	$205.8264	$205.83	$205.85	$205.80
Purchase #4	$80.87	11.503%	$90.1725	$90.17	$90.15	$90.20
Purchase #5	$17.45	4.789%	$18.2857	$18.29	$18.30	$18.30
Purchase #6	$204.90	9.395%	$224.1504	$224.15	$224.15	$224.20
Purchase #7	$152.38	7.288%	$163.4855	$163.49	$163.50	$163.50
7 purchase totals =	$903.58		$987.8445	$987.85	$987.90	$987.90