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	$36.72	10.586%	$40.6072	$40.61	$40.60	$40.60
Purchase #2	$53.38	12.215%	$59.9004	$59.90	$59.90	$59.90
Purchase #3	$32.72	5.534%	$34.5307	$34.53	$34.55	$34.50
Purchase #4	$203.84	13.257%	$230.8631	$230.86	$230.85	$230.90
Purchase #5	$57.67	5.480%	$60.8303	$60.83	$60.85	$60.80
Purchase #6	$195.33	10.415%	$215.6736	$215.67	$215.65	$215.70
Purchase #7	$68.49	11.588%	$76.4266	$76.43	$76.45	$76.40
7 purchase totals =	$648.15		$718.8319	$718.83	$718.85	$718.80