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	$226.27	9.814%	$248.4761	$248.48	$248.50	$248.50
Purchase #2	$31.64	9.333%	$34.593	$34.59	$34.60	$34.60
Purchase #3	$105.87	10.399%	$116.8794	$116.88	$116.90	$116.90
Purchase #4	$244.47	6.800%	$261.094	$261.09	$261.10	$261.10
Purchase #5	$217.51	11.238%	$241.9538	$241.95	$241.95	$242.00
Purchase #6	$148.91	4.684%	$155.8849	$155.88	$155.90	$155.90
Purchase #7	$31.78	3.292%	$32.8262	$32.83	$32.85	$32.80
7 purchase totals =	$1,006.45		$1,091.7074	$1,091.70	$1,091.80	$1,091.80