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	$72.50	13.126%	$82.0164	$82.02	$82.00	$82.00
Purchase #2	$34.30	8.321%	$37.1541	$37.15	$37.15	$37.20
Purchase #3	$241.64	4.452%	$252.3978	$252.40	$252.40	$252.40
Purchase #4	$45.92	4.555%	$48.0117	$48.01	$48.00	$48.00
Purchase #5	$83.95	12.678%	$94.5932	$94.59	$94.60	$94.60
Purchase #6	$135.94	6.591%	$144.8998	$144.90	$144.90	$144.90
Purchase #7	$164.95	4.781%	$172.8363	$172.84	$172.85	$172.80
7 purchase totals =	$779.20		$831.9093	$831.91	$831.90	$831.90