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	$82.50	7.710%	$88.8608	$88.86	$88.85	$88.90
Purchase #2	$209.55	12.436%	$235.6096	$235.61	$235.60	$235.60
Purchase #3	$9.42	12.367%	$10.585	$10.59	$10.60	$10.60
Purchase #4	$142.50	5.288%	$150.0354	$150.04	$150.05	$150.00
Purchase #5	$99.65	6.113%	$105.7416	$105.74	$105.75	$105.70
Purchase #6	$203.96	13.715%	$231.9331	$231.93	$231.95	$231.90
Purchase #7	$152.28	10.198%	$167.8095	$167.81	$167.80	$167.80
7 purchase totals =	$899.86		$990.5750	$990.58	$990.60	$990.50