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	$18.78	6.859%	$20.0681	$20.07	$20.05	$20.10
Purchase #2	$227.95	12.239%	$255.8488	$255.85	$255.85	$255.80
Purchase #3	$83.42	11.591%	$93.0892	$93.09	$93.10	$93.10
Purchase #4	$137.60	10.539%	$152.1017	$152.10	$152.10	$152.10
Purchase #5	$221.26	4.650%	$231.5486	$231.55	$231.55	$231.50
Purchase #6	$100.76	11.320%	$112.166	$112.17	$112.15	$112.20
Purchase #7	$204.61	9.573%	$224.1973	$224.20	$224.20	$224.20
7 purchase totals =	$994.38		$1,089.0197	$1,089.03	$1,089.00	$1,089.00