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	$202.96	10.169%	$223.599	$223.60	$223.60	$223.60
Purchase #2	$242.29	5.248%	$255.0054	$255.01	$255.00	$255.00
Purchase #3	$79.50	11.521%	$88.6592	$88.66	$88.65	$88.70
Purchase #4	$125.89	4.221%	$131.2038	$131.20	$131.20	$131.20
Purchase #5	$118.58	8.488%	$128.6451	$128.65	$128.65	$128.60
Purchase #6	$219.29	9.770%	$240.7146	$240.71	$240.70	$240.70
Purchase #7	$33.72	5.519%	$35.581	$35.58	$35.60	$35.60
7 purchase totals =	$1,022.23		$1,103.4081	$1,103.41	$1,103.40	$1,103.40