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	$92.87	10.505%	$102.626	$102.63	$102.65	$102.60
Purchase #2	$131.84	4.323%	$137.5394	$137.54	$137.55	$137.50
Purchase #3	$51.98	5.667%	$54.9257	$54.93	$54.95	$54.90
Purchase #4	$50.86	5.728%	$53.7733	$53.77	$53.75	$53.80
Purchase #5	$116.86	8.455%	$126.7405	$126.74	$126.75	$126.70
Purchase #6	$138.76	4.233%	$144.6337	$144.63	$144.65	$144.60
Purchase #7	$37.79	12.456%	$42.4971	$42.50	$42.50	$42.50
7 purchase totals =	$620.96		$662.7357	$662.74	$662.80	$662.60