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	$145.79	6.509%	$155.2795	$155.28	$155.30	$155.30
Purchase #2	$29.84	13.347%	$33.8227	$33.82	$33.80	$33.80
Purchase #3	$9.45	7.307%	$10.1405	$10.14	$10.15	$10.10
Purchase #4	$9.36	7.808%	$10.0908	$10.09	$10.10	$10.10
Purchase #5	$132.58	5.254%	$139.5458	$139.55	$139.55	$139.50
Purchase #6	$36.46	11.403%	$40.6175	$40.62	$40.60	$40.60
Purchase #7	$18.80	11.397%	$20.9426	$20.94	$20.95	$20.90
7 purchase totals =	$382.28		$410.4394	$410.44	$410.45	$410.30