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	$61.88	5.213%	$65.1058	$65.11	$65.10	$65.10
Purchase #2	$101.98	9.702%	$111.8741	$111.87	$111.85	$111.90
Purchase #3	$69.85	9.639%	$76.5828	$76.58	$76.60	$76.60
Purchase #4	$54.81	3.438%	$56.6944	$56.69	$56.70	$56.70
Purchase #5	$39.27	12.811%	$44.3009	$44.30	$44.30	$44.30
Purchase #6	$98.90	11.605%	$110.3773	$110.38	$110.40	$110.40
Purchase #7	$95.91	10.125%	$105.6209	$105.62	$105.60	$105.60
7 purchase totals =	$522.60		$570.5562	$570.55	$570.55	$570.60