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	$40.43	4.230%	$42.1402	$42.14	$42.15	$42.10
Purchase #2	$17.81	10.343%	$19.6521	$19.65	$19.65	$19.70
Purchase #3	$96.57	10.863%	$107.0604	$107.06	$107.05	$107.10
Purchase #4	$91.94	3.665%	$95.3096	$95.31	$95.30	$95.30
Purchase #5	$32.96	8.339%	$35.7085	$35.71	$35.70	$35.70
Purchase #6	$91.91	9.734%	$100.8565	$100.86	$100.85	$100.90
Purchase #7	$216.37	10.432%	$238.9417	$238.94	$238.95	$238.90
7 purchase totals =	$587.99		$639.6690	$639.67	$639.65	$639.70