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	$125.76	6.232%	$133.5974	$133.60	$133.60	$133.60
Purchase #2	$91.89	4.361%	$95.8973	$95.90	$95.90	$95.90
Purchase #3	$82.77	9.711%	$90.8078	$90.81	$90.80	$90.80
Purchase #4	$224.67	13.520%	$255.0454	$255.05	$255.05	$255.00
Purchase #5	$42.64	13.869%	$48.5537	$48.55	$48.55	$48.60
Purchase #6	$30.90	6.584%	$32.9345	$32.93	$32.95	$32.90
Purchase #7	$120.43	11.531%	$134.3168	$134.32	$134.30	$134.30
7 purchase totals =	$719.06		$791.1529	$791.16	$791.15	$791.10