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	$19.49	10.310%	$21.4994	$21.50	$21.50	$21.50
Purchase #2	$206.64	13.397%	$234.3236	$234.32	$234.30	$234.30
Purchase #3	$99.97	11.697%	$111.6635	$111.66	$111.65	$111.70
Purchase #4	$51.78	4.738%	$54.2333	$54.23	$54.25	$54.20
Purchase #5	$194.63	5.556%	$205.4436	$205.44	$205.45	$205.40
Purchase #6	$51.77	9.204%	$56.5349	$56.53	$56.55	$56.50
Purchase #7	$30.47	6.124%	$32.336	$32.34	$32.35	$32.30
7 purchase totals =	$654.75		$716.0343	$716.02	$716.05	$715.90