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	$95.72	13.115%	$108.2737	$108.27	$108.25	$108.30
Purchase #2	$150.45	11.107%	$167.1605	$167.16	$167.15	$167.20
Purchase #3	$11.81	8.839%	$12.8539	$12.85	$12.85	$12.90
Purchase #4	$17.48	13.371%	$19.8173	$19.82	$19.80	$19.80
Purchase #5	$29.89	9.677%	$32.7825	$32.78	$32.80	$32.80
Purchase #6	$216.77	11.240%	$241.1349	$241.13	$241.15	$241.10
Purchase #7	$143.25	12.278%	$160.8382	$160.84	$160.85	$160.80
7 purchase totals =	$665.37		$742.8610	$742.85	$742.85	$742.90