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	$91.89	8.283%	$99.5012	$99.50	$99.50	$99.50
Purchase #2	$163.76	13.749%	$186.2754	$186.28	$186.30	$186.30
Purchase #3	$185.86	10.626%	$205.6095	$205.61	$205.60	$205.60
Purchase #4	$111.93	7.539%	$120.3684	$120.37	$120.35	$120.40
Purchase #5	$40.75	10.248%	$44.9261	$44.93	$44.95	$44.90
Purchase #6	$126.65	13.634%	$143.9175	$143.92	$143.90	$143.90
Purchase #7	$98.29	11.584%	$109.6759	$109.68	$109.70	$109.70
7 purchase totals =	$819.13		$910.2740	$910.29	$910.30	$910.30