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	$138.53	6.505%	$147.5414	$147.54	$147.55	$147.50
Purchase #2	$20.91	3.597%	$21.6621	$21.66	$21.65	$21.70
Purchase #3	$241.72	6.128%	$256.5326	$256.53	$256.55	$256.50
Purchase #4	$139.55	3.626%	$144.6101	$144.61	$144.60	$144.60
Purchase #5	$27.75	5.420%	$29.2541	$29.25	$29.25	$29.30
Purchase #6	$83.69	13.482%	$94.9731	$94.97	$94.95	$95.00
Purchase #7	$78.61	13.863%	$89.5077	$89.51	$89.50	$89.50
7 purchase totals =	$730.76		$784.0811	$784.07	$784.05	$784.10