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	$41.97	4.417%	$43.8238	$43.82	$43.80	$43.80
Purchase #2	$131.36	6.162%	$139.4544	$139.45	$139.45	$139.50
Purchase #3	$47.53	3.411%	$49.1512	$49.15	$49.15	$49.20
Purchase #4	$58.59	13.255%	$66.3561	$66.36	$66.35	$66.40
Purchase #5	$6.30	13.328%	$7.1397	$7.14	$7.15	$7.10
Purchase #6	$75.89	10.621%	$83.9503	$83.95	$83.95	$84.00
Purchase #7	$85.50	6.364%	$90.9412	$90.94	$90.95	$90.90
7 purchase totals =	$447.14		$480.8167	$480.81	$480.80	$480.90