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	$6.62	11.818%	$7.4024	$7.40	$7.40	$7.40
Purchase #2	$63.74	4.724%	$66.7511	$66.75	$66.75	$66.80
Purchase #3	$129.59	12.617%	$145.9404	$145.94	$145.95	$145.90
Purchase #4	$11.96	3.730%	$12.4061	$12.41	$12.40	$12.40
Purchase #5	$105.82	5.443%	$111.5798	$111.58	$111.60	$111.60
Purchase #6	$124.85	12.180%	$140.0567	$140.06	$140.05	$140.10
Purchase #7	$115.70	12.712%	$130.4078	$130.41	$130.40	$130.40
7 purchase totals =	$558.28		$614.5443	$614.55	$614.55	$614.60