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	$16.81	5.574%	$17.747	$17.75	$17.75	$17.70
Purchase #2	$96.27	13.858%	$109.6111	$109.61	$109.60	$109.60
Purchase #3	$68.25	9.248%	$74.5618	$74.56	$74.55	$74.60
Purchase #4	$37.34	13.475%	$42.3716	$42.37	$42.35	$42.40
Purchase #5	$54.67	10.636%	$60.4847	$60.48	$60.50	$60.50
Purchase #6	$132.86	5.709%	$140.445	$140.45	$140.45	$140.40
Purchase #7	$132.67	3.555%	$137.3864	$137.39	$137.40	$137.40
7 purchase totals =	$538.87		$582.6076	$582.61	$582.60	$582.60