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	$35.39	13.306%	$40.099	$40.10	$40.10	$40.10
Purchase #2	$192.47	9.693%	$211.1261	$211.13	$211.15	$211.10
Purchase #3	$143.71	11.307%	$159.9593	$159.96	$159.95	$160.00
Purchase #4	$143.81	5.365%	$151.5254	$151.53	$151.55	$151.50
Purchase #5	$247.63	13.832%	$281.8822	$281.88	$281.90	$281.90
Purchase #6	$214.83	8.692%	$233.503	$233.50	$233.50	$233.50
Purchase #7	$76.99	7.649%	$82.879	$82.88	$82.90	$82.90
7 purchase totals =	$1,054.83		$1,160.9740	$1,160.98	$1,161.05	$1,161.00