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	$36.64	9.225%	$40.02	$40.02	$40.00	$40.00
Purchase #2	$72.42	8.231%	$78.3809	$78.38	$78.40	$78.40
Purchase #3	$113.98	12.820%	$128.5922	$128.59	$128.60	$128.60
Purchase #4	$31.75	7.602%	$34.1636	$34.16	$34.15	$34.20
Purchase #5	$182.74	5.239%	$192.3137	$192.31	$192.30	$192.30
Purchase #6	$151.61	10.243%	$167.1394	$167.14	$167.15	$167.10
Purchase #7	$172.31	7.319%	$184.9214	$184.92	$184.90	$184.90
7 purchase totals =	$761.45		$825.5312	$825.52	$825.50	$825.50