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	$132.86	4.657%	$139.0473	$139.05	$139.05	$139.00
Purchase #2	$158.96	8.746%	$172.8626	$172.86	$172.85	$172.90
Purchase #3	$54.72	3.659%	$56.7222	$56.72	$56.70	$56.70
Purchase #4	$40.71	4.228%	$42.4312	$42.43	$42.45	$42.40
Purchase #5	$113.94	6.540%	$121.3917	$121.39	$121.40	$121.40
Purchase #6	$9.32	7.859%	$10.0525	$10.05	$10.05	$10.10
Purchase #7	$32.75	12.231%	$36.7557	$36.76	$36.75	$36.80
7 purchase totals =	$543.26		$579.2632	$579.26	$579.25	$579.30