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	$210.96	13.769%	$240.0071	$240.01	$240.00	$240.00
Purchase #2	$90.73	10.312%	$100.0861	$100.09	$100.10	$100.10
Purchase #3	$93.38	8.128%	$100.9699	$100.97	$100.95	$101.00
Purchase #4	$54.84	7.722%	$59.0747	$59.07	$59.05	$59.10
Purchase #5	$103.75	3.613%	$107.4985	$107.50	$107.50	$107.50
Purchase #6	$106.82	6.281%	$113.5294	$113.53	$113.55	$113.50
Purchase #7	$160.43	11.480%	$178.8474	$178.85	$178.85	$178.80
7 purchase totals =	$820.91		$900.0131	$900.02	$900.00	$900.00