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	$33.25	6.826%	$35.5196	$35.52	$35.50	$35.50
Purchase #2	$60.84	11.177%	$67.6401	$67.64	$67.65	$67.60
Purchase #3	$142.39	4.671%	$149.041	$149.04	$149.05	$149.00
Purchase #4	$196.45	10.758%	$217.5841	$217.58	$217.60	$217.60
Purchase #5	$246.71	11.425%	$274.8966	$274.90	$274.90	$274.90
Purchase #6	$129.50	10.868%	$143.5741	$143.57	$143.55	$143.60
Purchase #7	$141.93	13.318%	$160.8322	$160.83	$160.85	$160.80
7 purchase totals =	$951.07		$1,049.0877	$1,049.08	$1,049.10	$1,049.00