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	$233.94	9.784%	$256.8287	$256.83	$256.85	$256.80
Purchase #2	$57.98	5.691%	$61.2796	$61.28	$61.30	$61.30
Purchase #3	$101.54	8.844%	$110.5202	$110.52	$110.50	$110.50
Purchase #4	$15.77	10.552%	$17.4341	$17.43	$17.45	$17.40
Purchase #5	$187.93	12.184%	$210.8274	$210.83	$210.85	$210.80
Purchase #6	$29.56	13.713%	$33.6136	$33.61	$33.60	$33.60
Purchase #7	$142.90	11.273%	$159.0091	$159.01	$159.00	$159.00
7 purchase totals =	$769.62		$849.5127	$849.51	$849.55	$849.40