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	$50.39	8.284%	$54.5643	$54.56	$54.55	$54.60
Purchase #2	$59.35	12.398%	$66.7082	$66.71	$66.70	$66.70
Purchase #3	$241.37	13.495%	$273.9429	$273.94	$273.95	$273.90
Purchase #4	$81.85	13.413%	$92.8285	$92.83	$92.85	$92.80
Purchase #5	$87.32	9.405%	$95.5324	$95.53	$95.55	$95.50
Purchase #6	$87.82	3.346%	$90.7585	$90.76	$90.75	$90.80
Purchase #7	$107.93	7.793%	$116.341	$116.34	$116.35	$116.30
7 purchase totals =	$716.03		$790.6758	$790.67	$790.70	$790.60