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	$68.86	11.250%	$76.6068	$76.61	$76.60	$76.60
Purchase #2	$88.26	4.752%	$92.4541	$92.45	$92.45	$92.50
Purchase #3	$55.69	6.514%	$59.3176	$59.32	$59.30	$59.30
Purchase #4	$164.44	7.766%	$177.2104	$177.21	$177.20	$177.20
Purchase #5	$145.92	9.700%	$160.0742	$160.07	$160.05	$160.10
Purchase #6	$92.43	8.210%	$100.0185	$100.02	$100.00	$100.00
Purchase #7	$12.66	12.747%	$14.2738	$14.27	$14.25	$14.30
7 purchase totals =	$628.26		$679.9554	$679.95	$679.85	$680.00