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	$117.45	9.658%	$128.7933	$128.79	$128.80	$128.80
Purchase #2	$89.60	11.657%	$100.0447	$100.04	$100.05	$100.00
Purchase #3	$17.41	11.849%	$19.4729	$19.47	$19.45	$19.50
Purchase #4	$223.94	5.800%	$236.9285	$236.93	$236.95	$236.90
Purchase #5	$214.77	12.196%	$240.9633	$240.96	$240.95	$241.00
Purchase #6	$21.73	10.541%	$24.0206	$24.02	$24.00	$24.00
Purchase #7	$215.55	3.625%	$223.3637	$223.36	$223.35	$223.40
7 purchase totals =	$900.45		$973.5870	$973.57	$973.55	$973.60