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	$8.86	7.402%	$9.5158	$9.52	$9.50	$9.50
Purchase #2	$121.40	5.144%	$127.6448	$127.64	$127.65	$127.60
Purchase #3	$50.77	5.682%	$53.6548	$53.65	$53.65	$53.70
Purchase #4	$109.39	10.235%	$120.5861	$120.59	$120.60	$120.60
Purchase #5	$78.43	4.677%	$82.0982	$82.10	$82.10	$82.10
Purchase #6	$46.78	10.277%	$51.5876	$51.59	$51.60	$51.60
Purchase #7	$99.69	13.278%	$112.9268	$112.93	$112.95	$112.90
7 purchase totals =	$515.32		$558.0141	$558.02	$558.05	$558.00