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	$32.48	8.149%	$35.1268	$35.13	$35.15	$35.10
Purchase #2	$36.95	3.249%	$38.1505	$38.15	$38.15	$38.20
Purchase #3	$103.25	7.872%	$111.3778	$111.38	$111.40	$111.40
Purchase #4	$110.42	12.764%	$124.514	$124.51	$124.50	$124.50
Purchase #5	$202.83	6.839%	$216.7015	$216.70	$216.70	$216.70
Purchase #6	$183.57	11.590%	$204.8458	$204.85	$204.85	$204.80
Purchase #7	$172.65	7.209%	$185.0963	$185.10	$185.10	$185.10
7 purchase totals =	$842.15		$915.8127	$915.82	$915.85	$915.80