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	$65.77	9.594%	$72.08	$72.08	$72.10	$72.10
Purchase #2	$85.38	11.763%	$95.4232	$95.42	$95.40	$95.40
Purchase #3	$142.72	9.462%	$156.2242	$156.22	$156.20	$156.20
Purchase #4	$120.43	10.392%	$132.9451	$132.95	$132.95	$132.90
Purchase #5	$115.77	13.248%	$131.1072	$131.11	$131.10	$131.10
Purchase #6	$68.27	6.213%	$72.5116	$72.51	$72.50	$72.50
Purchase #7	$35.92	9.592%	$39.3654	$39.37	$39.35	$39.40
7 purchase totals =	$634.26		$699.6567	$699.66	$699.60	$699.60