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	$103.85	7.401%	$111.5359	$111.54	$111.55	$111.50
Purchase #2	$155.86	8.108%	$168.4971	$168.50	$168.50	$168.50
Purchase #3	$36.45	12.348%	$40.9508	$40.95	$40.95	$41.00
Purchase #4	$200.79	3.321%	$207.4582	$207.46	$207.45	$207.50
Purchase #5	$196.42	12.474%	$220.9214	$220.92	$220.90	$220.90
Purchase #6	$12.66	9.249%	$13.8309	$13.83	$13.85	$13.80
Purchase #7	$106.79	11.185%	$118.7345	$118.73	$118.75	$118.70
7 purchase totals =	$812.82		$881.9288	$881.93	$881.95	$881.90