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	$7.54	12.706%	$8.498	$8.50	$8.50	$8.50
Purchase #2	$32.75	13.825%	$37.2777	$37.28	$37.30	$37.30
Purchase #3	$76.29	5.306%	$80.3379	$80.34	$80.35	$80.30
Purchase #4	$115.56	5.472%	$121.8834	$121.88	$121.90	$121.90
Purchase #5	$9.78	5.254%	$10.2938	$10.29	$10.30	$10.30
Purchase #6	$138.78	8.509%	$150.5888	$150.59	$150.60	$150.60
Purchase #7	$45.39	13.338%	$51.4441	$51.44	$51.45	$51.40
7 purchase totals =	$426.09		$460.3237	$460.32	$460.40	$460.30