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	$137.55	4.734%	$144.0616	$144.06	$144.05	$144.10
Purchase #2	$40.37	12.699%	$45.4966	$45.50	$45.50	$45.50
Purchase #3	$157.83	6.504%	$168.0953	$168.10	$168.10	$168.10
Purchase #4	$42.96	5.747%	$45.4289	$45.43	$45.45	$45.40
Purchase #5	$70.97	11.440%	$79.089	$79.09	$79.10	$79.10
Purchase #6	$103.67	13.342%	$117.5017	$117.50	$117.50	$117.50
Purchase #7	$39.53	11.816%	$44.2009	$44.20	$44.20	$44.20
7 purchase totals =	$592.88		$643.8740	$643.88	$643.90	$643.90