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	$163.82	13.766%	$186.3715	$186.37	$186.35	$186.40
Purchase #2	$80.80	11.784%	$90.3215	$90.32	$90.30	$90.30
Purchase #3	$207.85	11.576%	$231.9107	$231.91	$231.90	$231.90
Purchase #4	$172.78	11.504%	$192.6566	$192.66	$192.65	$192.70
Purchase #5	$223.35	5.821%	$236.3512	$236.35	$236.35	$236.40
Purchase #6	$61.93	8.563%	$67.2331	$67.23	$67.25	$67.20
Purchase #7	$158.97	5.633%	$167.9248	$167.92	$167.90	$167.90
7 purchase totals =	$1,069.50		$1,172.7694	$1,172.76	$1,172.70	$1,172.80