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	$78.91	13.127%	$89.2685	$89.27	$89.25	$89.30
Purchase #2	$47.86	9.264%	$52.2938	$52.29	$52.30	$52.30
Purchase #3	$50.68	11.169%	$56.3404	$56.34	$56.35	$56.30
Purchase #4	$152.51	6.738%	$162.7861	$162.79	$162.80	$162.80
Purchase #5	$196.29	10.821%	$217.5305	$217.53	$217.55	$217.50
Purchase #6	$233.67	11.634%	$260.8552	$260.86	$260.85	$260.90
Purchase #7	$242.32	7.591%	$260.7145	$260.71	$260.70	$260.70
7 purchase totals =	$1,002.24		$1,099.7890	$1,099.79	$1,099.80	$1,099.80