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	$37.29	9.738%	$40.9213	$40.92	$40.90	$40.90
Purchase #2	$100.54	10.861%	$111.4596	$111.46	$111.45	$111.50
Purchase #3	$7.98	4.262%	$8.3201	$8.32	$8.30	$8.30
Purchase #4	$166.76	5.197%	$175.4265	$175.43	$175.45	$175.40
Purchase #5	$112.61	10.697%	$124.6559	$124.66	$124.65	$124.70
Purchase #6	$237.65	13.327%	$269.3216	$269.32	$269.30	$269.30
Purchase #7	$206.81	10.146%	$227.7929	$227.79	$227.80	$227.80
7 purchase totals =	$869.64		$957.8979	$957.90	$957.85	$957.90