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	$123.76	7.136%	$132.5915	$132.59	$132.60	$132.60
Purchase #2	$60.39	11.217%	$67.1639	$67.16	$67.15	$67.20
Purchase #3	$244.39	4.538%	$255.4804	$255.48	$255.50	$255.50
Purchase #4	$149.26	7.445%	$160.3724	$160.37	$160.35	$160.40
Purchase #5	$15.61	10.781%	$17.2929	$17.29	$17.30	$17.30
Purchase #6	$55.27	11.545%	$61.6509	$61.65	$61.65	$61.70
Purchase #7	$169.29	12.832%	$191.0133	$191.01	$191.00	$191.00
7 purchase totals =	$817.97		$885.5653	$885.55	$885.55	$885.70