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	$14.64	13.295%	$16.5864	$16.59	$16.60	$16.60
Purchase #2	$34.82	5.633%	$36.7814	$36.78	$36.80	$36.80
Purchase #3	$229.71	12.762%	$259.0256	$259.03	$259.05	$259.00
Purchase #4	$111.31	8.355%	$120.61	$120.61	$120.60	$120.60
Purchase #5	$50.33	4.426%	$52.5576	$52.56	$52.55	$52.60
Purchase #6	$141.84	10.399%	$156.5899	$156.59	$156.60	$156.60
Purchase #7	$111.37	6.305%	$118.3919	$118.39	$118.40	$118.40
7 purchase totals =	$694.02		$760.5428	$760.55	$760.60	$760.60