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	$28.67	13.577%	$32.5625	$32.56	$32.55	$32.60
Purchase #2	$41.50	13.594%	$47.1415	$47.14	$47.15	$47.10
Purchase #3	$248.92	3.129%	$256.7087	$256.71	$256.70	$256.70
Purchase #4	$157.53	13.714%	$179.1337	$179.13	$179.15	$179.10
Purchase #5	$172.94	3.248%	$178.5571	$178.56	$178.55	$178.60
Purchase #6	$32.95	8.521%	$35.7577	$35.76	$35.75	$35.80
Purchase #7	$192.77	4.103%	$200.6794	$200.68	$200.70	$200.70
7 purchase totals =	$875.28		$930.5406	$930.54	$930.55	$930.60