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	$63.90	3.318%	$66.0202	$66.02	$66.00	$66.00
Purchase #2	$174.38	12.683%	$196.4966	$196.50	$196.50	$196.50
Purchase #3	$217.64	7.849%	$234.7226	$234.72	$234.70	$234.70
Purchase #4	$55.60	3.174%	$57.3647	$57.36	$57.35	$57.40
Purchase #5	$13.71	7.617%	$14.7543	$14.75	$14.75	$14.80
Purchase #6	$56.37	9.234%	$61.5752	$61.58	$61.60	$61.60
Purchase #7	$51.59	11.703%	$57.6276	$57.63	$57.65	$57.60
7 purchase totals =	$633.19		$688.5612	$688.56	$688.55	$688.60