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	$37.60	6.305%	$39.9707	$39.97	$39.95	$40.00
Purchase #2	$157.31	4.312%	$164.0932	$164.09	$164.10	$164.10
Purchase #3	$178.95	6.210%	$190.0628	$190.06	$190.05	$190.10
Purchase #4	$202.66	3.631%	$210.0186	$210.02	$210.00	$210.00
Purchase #5	$105.96	3.521%	$109.6909	$109.69	$109.70	$109.70
Purchase #6	$52.97	5.225%	$55.7377	$55.74	$55.75	$55.70
Purchase #7	$99.59	12.272%	$111.8117	$111.81	$111.80	$111.80
7 purchase totals =	$835.04		$881.3856	$881.38	$881.35	$881.40