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	$27.56	13.469%	$31.2721	$31.27	$31.25	$31.30
Purchase #2	$84.91	13.162%	$96.0859	$96.09	$96.10	$96.10
Purchase #3	$172.43	7.316%	$185.045	$185.05	$185.05	$185.00
Purchase #4	$46.92	8.407%	$50.8646	$50.86	$50.85	$50.90
Purchase #5	$185.75	10.616%	$205.4692	$205.47	$205.45	$205.50
Purchase #6	$137.27	4.341%	$143.2289	$143.23	$143.25	$143.20
Purchase #7	$213.74	12.820%	$241.1415	$241.14	$241.15	$241.10
7 purchase totals =	$868.58		$953.1072	$953.11	$953.10	$953.10