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	$217.64	9.684%	$238.7163	$238.72	$238.70	$238.70
Purchase #2	$225.43	6.266%	$239.5554	$239.56	$239.55	$239.60
Purchase #3	$141.27	7.391%	$151.7113	$151.71	$151.70	$151.70
Purchase #4	$9.65	9.730%	$10.5889	$10.59	$10.60	$10.60
Purchase #5	$67.57	11.683%	$75.4642	$75.46	$75.45	$75.50
Purchase #6	$80.74	10.623%	$89.317	$89.32	$89.30	$89.30
Purchase #7	$68.51	13.787%	$77.9555	$77.96	$77.95	$78.00
7 purchase totals =	$810.81		$883.3086	$883.32	$883.25	$883.40