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	$122.53	6.305%	$130.2555	$130.26	$130.25	$130.30
Purchase #2	$131.57	12.337%	$147.8018	$147.80	$147.80	$147.80
Purchase #3	$172.32	6.540%	$183.5897	$183.59	$183.60	$183.60
Purchase #4	$92.27	11.771%	$103.1311	$103.13	$103.15	$103.10
Purchase #5	$6.27	13.739%	$7.1314	$7.13	$7.15	$7.10
Purchase #6	$89.81	12.531%	$101.0641	$101.06	$101.05	$101.10
Purchase #7	$104.65	6.811%	$111.7777	$111.78	$111.80	$111.80
7 purchase totals =	$719.42		$784.7513	$784.75	$784.80	$784.80