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	$28.61	11.377%	$31.865	$31.87	$31.85	$31.90
Purchase #2	$5.81	11.613%	$6.4847	$6.48	$6.50	$6.50
Purchase #3	$21.50	13.203%	$24.3386	$24.34	$24.35	$24.30
Purchase #4	$171.97	3.807%	$178.5169	$178.52	$178.50	$178.50
Purchase #5	$39.26	9.861%	$43.1314	$43.13	$43.15	$43.10
Purchase #6	$217.30	4.726%	$227.5696	$227.57	$227.55	$227.60
Purchase #7	$68.51	6.425%	$72.9118	$72.91	$72.90	$72.90
7 purchase totals =	$552.96		$584.8180	$584.82	$584.80	$584.80