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	$212.39	7.650%	$228.6378	$228.64	$228.65	$228.60
Purchase #2	$85.88	4.265%	$89.5428	$89.54	$89.55	$89.50
Purchase #3	$17.65	11.236%	$19.6332	$19.63	$19.65	$19.60
Purchase #4	$37.26	9.851%	$40.9305	$40.93	$40.95	$40.90
Purchase #5	$54.84	13.184%	$62.0701	$62.07	$62.05	$62.10
Purchase #6	$189.77	11.845%	$212.2483	$212.25	$212.25	$212.20
Purchase #7	$112.53	12.836%	$126.9744	$126.97	$126.95	$127.00
7 purchase totals =	$710.32		$780.0371	$780.03	$780.05	$779.90