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	$87.55	3.392%	$90.5197	$90.52	$90.50	$90.50
Purchase #2	$37.51	4.579%	$39.2276	$39.23	$39.25	$39.20
Purchase #3	$170.70	5.398%	$179.9144	$179.91	$179.90	$179.90
Purchase #4	$70.46	11.539%	$78.5904	$78.59	$78.60	$78.60
Purchase #5	$72.25	12.345%	$81.1693	$81.17	$81.15	$81.20
Purchase #6	$17.81	11.353%	$19.832	$19.83	$19.85	$19.80
Purchase #7	$194.78	10.341%	$214.9222	$214.92	$214.90	$214.90
7 purchase totals =	$651.06		$704.1756	$704.17	$704.15	$704.10