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	$239.69	6.713%	$255.7804	$255.78	$255.80	$255.80
Purchase #2	$100.61	10.591%	$111.2656	$111.27	$111.25	$111.30
Purchase #3	$223.92	11.353%	$249.3416	$249.34	$249.35	$249.30
Purchase #4	$100.96	11.411%	$112.4805	$112.48	$112.50	$112.50
Purchase #5	$18.35	7.684%	$19.76	$19.76	$19.75	$19.80
Purchase #6	$156.89	8.383%	$170.0421	$170.04	$170.05	$170.00
Purchase #7	$242.78	3.754%	$251.894	$251.89	$251.90	$251.90
7 purchase totals =	$1,083.20		$1,170.5642	$1,170.56	$1,170.60	$1,170.60