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	$215.77	11.462%	$240.5016	$240.50	$240.50	$240.50
Purchase #2	$134.69	11.836%	$150.6319	$150.63	$150.65	$150.60
Purchase #3	$172.89	9.220%	$188.8305	$188.83	$188.85	$188.80
Purchase #4	$192.62	7.683%	$207.419	$207.42	$207.40	$207.40
Purchase #5	$134.85	7.179%	$144.5309	$144.53	$144.55	$144.50
Purchase #6	$95.94	8.758%	$104.3424	$104.34	$104.35	$104.30
Purchase #7	$32.56	3.291%	$33.6315	$33.63	$33.65	$33.60
7 purchase totals =	$979.32		$1,069.8878	$1,069.88	$1,069.95	$1,069.70