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	$248.87	12.438%	$279.8245	$279.82	$279.80	$279.80
Purchase #2	$132.62	4.743%	$138.9102	$138.91	$138.90	$138.90
Purchase #3	$94.91	4.177%	$98.8744	$98.87	$98.85	$98.90
Purchase #4	$191.46	9.609%	$209.8574	$209.86	$209.85	$209.90
Purchase #5	$238.98	10.136%	$263.203	$263.20	$263.20	$263.20
Purchase #6	$161.81	6.602%	$172.4927	$172.49	$172.50	$172.50
Purchase #7	$103.91	7.665%	$111.8747	$111.87	$111.85	$111.90
7 purchase totals =	$1,172.56		$1,275.0369	$1,275.02	$1,274.95	$1,275.10