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	$68.29	9.861%	$75.0241	$75.02	$75.00	$75.00
Purchase #2	$142.90	5.389%	$150.6009	$150.60	$150.60	$150.60
Purchase #3	$127.25	6.144%	$135.0682	$135.07	$135.05	$135.10
Purchase #4	$115.85	10.393%	$127.8903	$127.89	$127.90	$127.90
Purchase #5	$54.70	8.609%	$59.4091	$59.41	$59.40	$59.40
Purchase #6	$46.31	13.325%	$52.4808	$52.48	$52.50	$52.50
Purchase #7	$87.75	9.398%	$95.9967	$96.00	$96.00	$96.00
7 purchase totals =	$643.05		$696.4701	$696.47	$696.45	$696.50