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	$49.65	12.873%	$56.0414	$56.04	$56.05	$56.00
Purchase #2	$26.62	11.161%	$29.5911	$29.59	$29.60	$29.60
Purchase #3	$136.89	11.345%	$152.4202	$152.42	$152.40	$152.40
Purchase #4	$99.58	3.710%	$103.2744	$103.27	$103.25	$103.30
Purchase #5	$24.43	10.794%	$27.067	$27.07	$27.05	$27.10
Purchase #6	$94.78	10.626%	$104.8513	$104.85	$104.85	$104.90
Purchase #7	$146.61	7.221%	$157.1967	$157.20	$157.20	$157.20
7 purchase totals =	$578.56		$630.4421	$630.44	$630.40	$630.50