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	$160.88	11.558%	$179.4745	$179.47	$179.45	$179.50
Purchase #2	$33.69	4.612%	$35.2438	$35.24	$35.25	$35.20
Purchase #3	$240.27	6.796%	$256.5987	$256.60	$256.60	$256.60
Purchase #4	$159.84	8.325%	$173.1467	$173.15	$173.15	$173.10
Purchase #5	$157.92	9.372%	$172.7203	$172.72	$172.70	$172.70
Purchase #6	$247.93	10.778%	$274.6519	$274.65	$274.65	$274.70
Purchase #7	$200.28	12.402%	$225.1187	$225.12	$225.10	$225.10
7 purchase totals =	$1,200.81		$1,316.9546	$1,316.95	$1,316.90	$1,316.90