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	$52.71	13.420%	$59.7837	$59.78	$59.80	$59.80
Purchase #2	$90.45	9.229%	$98.7976	$98.80	$98.80	$98.80
Purchase #3	$54.96	8.752%	$59.7701	$59.77	$59.75	$59.80
Purchase #4	$200.99	4.198%	$209.4276	$209.43	$209.45	$209.40
Purchase #5	$242.66	6.304%	$257.9573	$257.96	$257.95	$258.00
Purchase #6	$170.94	8.711%	$185.8306	$185.83	$185.85	$185.80
Purchase #7	$161.90	10.602%	$179.0646	$179.06	$179.05	$179.10
7 purchase totals =	$974.61		$1,050.6315	$1,050.63	$1,050.65	$1,050.70