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	$102.82	13.671%	$116.8765	$116.88	$116.90	$116.90
Purchase #2	$30.34	7.670%	$32.6671	$32.67	$32.65	$32.70
Purchase #3	$228.77	4.509%	$239.0852	$239.09	$239.10	$239.10
Purchase #4	$132.59	13.309%	$150.2364	$150.24	$150.25	$150.20
Purchase #5	$213.96	7.444%	$229.8872	$229.89	$229.90	$229.90
Purchase #6	$45.80	6.796%	$48.9126	$48.91	$48.90	$48.90
Purchase #7	$173.42	8.166%	$187.5815	$187.58	$187.60	$187.60
7 purchase totals =	$927.70		$1,005.2465	$1,005.26	$1,005.30	$1,005.30