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	$15.91	11.408%	$17.725	$17.73	$17.75	$17.70
Purchase #2	$241.31	11.585%	$269.2658	$269.27	$269.25	$269.30
Purchase #3	$127.37	10.597%	$140.8674	$140.87	$140.85	$140.90
Purchase #4	$40.89	4.440%	$42.7055	$42.71	$42.70	$42.70
Purchase #5	$166.93	11.171%	$185.5778	$185.58	$185.60	$185.60
Purchase #6	$39.41	6.751%	$42.0706	$42.07	$42.05	$42.10
Purchase #7	$66.28	3.626%	$68.6833	$68.68	$68.70	$68.70
7 purchase totals =	$698.10		$766.8954	$766.91	$766.90	$767.00