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	$132.69	5.452%	$139.9243	$139.92	$139.90	$139.90
Purchase #2	$82.43	4.117%	$85.8236	$85.82	$85.80	$85.80
Purchase #3	$172.48	10.215%	$190.0988	$190.10	$190.10	$190.10
Purchase #4	$127.45	12.516%	$143.4016	$143.40	$143.40	$143.40
Purchase #5	$207.74	5.370%	$218.8956	$218.90	$218.90	$218.90
Purchase #6	$5.74	3.239%	$5.9259	$5.93	$5.95	$5.90
Purchase #7	$32.28	6.867%	$34.4967	$34.50	$34.50	$34.50
7 purchase totals =	$760.81		$818.5665	$818.57	$818.55	$818.50