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	$27.57	4.751%	$28.8799	$28.88	$28.90	$28.90
Purchase #2	$42.96	5.549%	$45.3439	$45.34	$45.35	$45.30
Purchase #3	$31.88	7.757%	$34.3529	$34.35	$34.35	$34.40
Purchase #4	$78.99	10.574%	$87.3424	$87.34	$87.35	$87.30
Purchase #5	$132.64	9.829%	$145.6772	$145.68	$145.70	$145.70
Purchase #6	$56.80	9.317%	$62.0921	$62.09	$62.10	$62.10
Purchase #7	$91.45	10.265%	$100.8373	$100.84	$100.85	$100.80
7 purchase totals =	$462.29		$504.5257	$504.52	$504.60	$504.50