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	$59.61	9.858%	$65.4864	$65.49	$65.50	$65.50
Purchase #2	$225.76	3.841%	$234.4314	$234.43	$234.45	$234.40
Purchase #3	$19.64	10.490%	$21.7002	$21.70	$21.70	$21.70
Purchase #4	$52.26	5.145%	$54.9488	$54.95	$54.95	$54.90
Purchase #5	$108.59	3.639%	$112.5416	$112.54	$112.55	$112.50
Purchase #6	$136.69	3.828%	$141.9225	$141.92	$141.90	$141.90
Purchase #7	$178.38	12.607%	$200.8684	$200.87	$200.85	$200.90
7 purchase totals =	$780.93		$831.8993	$831.90	$831.90	$831.80