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	$63.66	12.124%	$71.3781	$71.38	$71.40	$71.40
Purchase #2	$170.65	11.635%	$190.5051	$190.51	$190.50	$190.50
Purchase #3	$152.25	10.798%	$168.69	$168.69	$168.70	$168.70
Purchase #4	$60.36	9.176%	$65.8986	$65.90	$65.90	$65.90
Purchase #5	$192.47	10.290%	$212.2752	$212.28	$212.30	$212.30
Purchase #6	$10.47	5.618%	$11.0582	$11.06	$11.05	$11.10
Purchase #7	$19.38	12.642%	$21.83	$21.83	$21.85	$21.80
7 purchase totals =	$669.24		$741.6352	$741.65	$741.70	$741.70