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	$51.60	8.866%	$56.1749	$56.17	$56.15	$56.20
Purchase #2	$147.77	8.507%	$160.3408	$160.34	$160.35	$160.30
Purchase #3	$236.39	7.794%	$254.8142	$254.81	$254.80	$254.80
Purchase #4	$207.72	7.195%	$222.6655	$222.67	$222.65	$222.70
Purchase #5	$10.59	13.429%	$12.0121	$12.01	$12.00	$12.00
Purchase #6	$10.92	10.453%	$12.0615	$12.06	$12.05	$12.10
Purchase #7	$145.42	3.373%	$150.325	$150.33	$150.35	$150.30
7 purchase totals =	$810.41		$868.3940	$868.39	$868.35	$868.40