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	$128.37	11.807%	$143.5266	$143.53	$143.55	$143.50
Purchase #2	$102.75	7.143%	$110.0894	$110.09	$110.10	$110.10
Purchase #3	$77.47	9.522%	$84.8467	$84.85	$84.85	$84.80
Purchase #4	$167.95	3.500%	$173.8283	$173.83	$173.85	$173.80
Purchase #5	$204.94	3.398%	$211.9039	$211.90	$211.90	$211.90
Purchase #6	$46.61	13.253%	$52.7872	$52.79	$52.80	$52.80
Purchase #7	$78.87	13.241%	$89.3132	$89.31	$89.30	$89.30
7 purchase totals =	$806.96		$866.2953	$866.30	$866.35	$866.20