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	$166.39	4.148%	$173.2919	$173.29	$173.30	$173.30
Purchase #2	$113.52	8.605%	$123.2884	$123.29	$123.30	$123.30
Purchase #3	$112.39	5.260%	$118.3017	$118.30	$118.30	$118.30
Purchase #4	$214.93	9.624%	$235.6149	$235.61	$235.60	$235.60
Purchase #5	$200.26	11.193%	$222.6751	$222.68	$222.70	$222.70
Purchase #6	$31.61	11.713%	$35.3125	$35.31	$35.30	$35.30
Purchase #7	$225.99	5.520%	$238.4646	$238.46	$238.45	$238.50
7 purchase totals =	$1,065.09		$1,146.9491	$1,146.94	$1,146.95	$1,147.00