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	$131.35	6.183%	$139.4714	$139.47	$139.45	$139.50
Purchase #2	$32.83	6.722%	$35.0368	$35.04	$35.05	$35.00
Purchase #3	$99.32	11.830%	$111.0696	$111.07	$111.05	$111.10
Purchase #4	$240.54	5.617%	$254.0511	$254.05	$254.05	$254.10
Purchase #5	$144.38	8.295%	$156.3563	$156.36	$156.35	$156.40
Purchase #6	$219.47	12.458%	$246.8116	$246.81	$246.80	$246.80
Purchase #7	$32.57	9.313%	$35.6032	$35.60	$35.60	$35.60
7 purchase totals =	$900.46		$978.4000	$978.40	$978.35	$978.50