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	$95.87	3.717%	$99.4335	$99.43	$99.45	$99.40
Purchase #2	$140.85	5.689%	$148.863	$148.86	$148.85	$148.90
Purchase #3	$16.76	11.460%	$18.6807	$18.68	$18.70	$18.70
Purchase #4	$23.96	7.633%	$25.7889	$25.79	$25.80	$25.80
Purchase #5	$19.57	8.215%	$21.1777	$21.18	$21.20	$21.20
Purchase #6	$180.85	10.733%	$200.2606	$200.26	$200.25	$200.30
Purchase #7	$125.85	5.613%	$132.914	$132.91	$132.90	$132.90
7 purchase totals =	$603.71		$647.1184	$647.11	$647.15	$647.20