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	$53.86	10.638%	$59.5896	$59.59	$59.60	$59.60
Purchase #2	$229.69	11.366%	$255.7966	$255.80	$255.80	$255.80
Purchase #3	$227.56	6.384%	$242.0874	$242.09	$242.10	$242.10
Purchase #4	$207.39	3.756%	$215.1796	$215.18	$215.20	$215.20
Purchase #5	$30.55	6.186%	$32.4398	$32.44	$32.45	$32.40
Purchase #6	$116.36	6.866%	$124.3493	$124.35	$124.35	$124.30
Purchase #7	$162.85	4.736%	$170.5626	$170.56	$170.55	$170.60
7 purchase totals =	$1,028.26		$1,100.0049	$1,100.01	$1,100.05	$1,100.00