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	$166.42	11.749%	$185.9727	$185.97	$185.95	$186.00
Purchase #2	$78.61	12.719%	$88.6084	$88.61	$88.60	$88.60
Purchase #3	$172.89	7.324%	$185.5525	$185.55	$185.55	$185.60
Purchase #4	$35.72	9.168%	$38.9948	$38.99	$39.00	$39.00
Purchase #5	$132.61	13.192%	$150.1039	$150.10	$150.10	$150.10
Purchase #6	$217.93	7.798%	$234.9242	$234.92	$234.90	$234.90
Purchase #7	$184.93	7.300%	$198.4299	$198.43	$198.45	$198.40
7 purchase totals =	$989.11		$1,082.5864	$1,082.57	$1,082.55	$1,082.60