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	$76.48	3.144%	$78.8845	$78.88	$78.90	$78.90
Purchase #2	$63.73	4.305%	$66.4736	$66.47	$66.45	$66.50
Purchase #3	$114.29	11.758%	$127.7282	$127.73	$127.75	$127.70
Purchase #4	$63.58	5.111%	$66.8296	$66.83	$66.85	$66.80
Purchase #5	$240.82	7.426%	$258.7033	$258.70	$258.70	$258.70
Purchase #6	$186.67	13.158%	$211.232	$211.23	$211.25	$211.20
Purchase #7	$209.41	3.747%	$217.2566	$217.26	$217.25	$217.30
7 purchase totals =	$954.98		$1,027.1078	$1,027.10	$1,027.15	$1,027.10