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	$43.37	4.613%	$45.3707	$45.37	$45.35	$45.40
Purchase #2	$66.80	7.830%	$72.0304	$72.03	$72.05	$72.00
Purchase #3	$130.86	5.273%	$137.7602	$137.76	$137.75	$137.80
Purchase #4	$217.43	9.857%	$238.8621	$238.86	$238.85	$238.90
Purchase #5	$12.45	4.208%	$12.9739	$12.97	$12.95	$13.00
Purchase #6	$5.98	7.221%	$6.4118	$6.41	$6.40	$6.40
Purchase #7	$27.92	7.624%	$30.0486	$30.05	$30.05	$30.00
7 purchase totals =	$504.81		$543.4577	$543.45	$543.40	$543.50