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	$187.93	11.428%	$209.4066	$209.41	$209.40	$209.40
Purchase #2	$55.47	9.870%	$60.9449	$60.94	$60.95	$60.90
Purchase #3	$115.82	12.840%	$130.6913	$130.69	$130.70	$130.70
Purchase #4	$221.93	5.704%	$234.5889	$234.59	$234.60	$234.60
Purchase #5	$126.89	4.676%	$132.8234	$132.82	$132.80	$132.80
Purchase #6	$105.61	5.291%	$111.1978	$111.20	$111.20	$111.20
Purchase #7	$113.52	8.319%	$122.9637	$122.96	$122.95	$123.00
7 purchase totals =	$927.17		$1,002.6166	$1,002.61	$1,002.60	$1,002.60