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	$93.43	6.489%	$99.4927	$99.49	$99.50	$99.50
Purchase #2	$121.32	8.712%	$131.8894	$131.89	$131.90	$131.90
Purchase #3	$171.94	3.169%	$177.3888	$177.39	$177.40	$177.40
Purchase #4	$190.83	10.105%	$210.1134	$210.11	$210.10	$210.10
Purchase #5	$80.61	6.212%	$85.6175	$85.62	$85.60	$85.60
Purchase #6	$142.32	12.748%	$160.463	$160.46	$160.45	$160.50
Purchase #7	$51.73	4.745%	$54.1846	$54.18	$54.20	$54.20
7 purchase totals =	$852.18		$919.1494	$919.14	$919.15	$919.20