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	$31.59	11.841%	$35.3306	$35.33	$35.35	$35.30
Purchase #2	$230.41	4.792%	$241.4512	$241.45	$241.45	$241.50
Purchase #3	$139.74	10.168%	$153.9488	$153.95	$153.95	$153.90
Purchase #4	$236.27	7.331%	$253.591	$253.59	$253.60	$253.60
Purchase #5	$160.54	4.388%	$167.5845	$167.58	$167.60	$167.60
Purchase #6	$73.51	13.385%	$83.3493	$83.35	$83.35	$83.30
Purchase #7	$30.60	10.161%	$33.7093	$33.71	$33.70	$33.70
7 purchase totals =	$902.66		$968.9647	$968.96	$969.00	$968.90