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	$220.54	12.585%	$248.295	$248.30	$248.30	$248.30
Purchase #2	$118.25	10.870%	$131.1038	$131.10	$131.10	$131.10
Purchase #3	$116.46	11.329%	$129.6538	$129.65	$129.65	$129.70
Purchase #4	$84.57	13.509%	$95.9946	$95.99	$96.00	$96.00
Purchase #5	$85.98	4.558%	$89.899	$89.90	$89.90	$89.90
Purchase #6	$71.30	7.827%	$76.8807	$76.88	$76.90	$76.90
Purchase #7	$220.43	9.367%	$241.0777	$241.08	$241.10	$241.10
7 purchase totals =	$917.53		$1,012.9046	$1,012.90	$1,012.95	$1,013.00