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	$104.96	7.206%	$112.5234	$112.52	$112.50	$112.50
Purchase #2	$237.49	12.130%	$266.2975	$266.30	$266.30	$266.30
Purchase #3	$54.75	8.800%	$59.568	$59.57	$59.55	$59.60
Purchase #4	$244.56	10.301%	$269.7521	$269.75	$269.75	$269.80
Purchase #5	$128.35	7.339%	$137.7696	$137.77	$137.75	$137.80
Purchase #6	$7.87	13.215%	$8.91	$8.91	$8.90	$8.90
Purchase #7	$212.87	6.664%	$227.0557	$227.06	$227.05	$227.10
7 purchase totals =	$990.85		$1,081.8763	$1,081.88	$1,081.80	$1,082.00