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	$35.58	13.294%	$40.31	$40.31	$40.30	$40.30
Purchase #2	$126.79	10.357%	$139.9216	$139.92	$139.90	$139.90
Purchase #3	$239.86	8.104%	$259.2983	$259.30	$259.30	$259.30
Purchase #4	$45.96	11.286%	$51.147	$51.15	$51.15	$51.10
Purchase #5	$230.37	10.396%	$254.3193	$254.32	$254.30	$254.30
Purchase #6	$57.76	3.509%	$59.7868	$59.79	$59.80	$59.80
Purchase #7	$142.44	12.484%	$160.2222	$160.22	$160.20	$160.20
7 purchase totals =	$878.76		$965.0052	$965.01	$964.95	$964.90