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	$29.83	7.334%	$32.0177	$32.02	$32.00	$32.00
Purchase #2	$121.88	13.811%	$138.7128	$138.71	$138.70	$138.70
Purchase #3	$226.82	12.867%	$256.0049	$256.00	$256.00	$256.00
Purchase #4	$27.75	4.136%	$28.8977	$28.90	$28.90	$28.90
Purchase #5	$121.40	7.633%	$130.6665	$130.67	$130.65	$130.70
Purchase #6	$121.42	9.446%	$132.8893	$132.89	$132.90	$132.90
Purchase #7	$95.72	9.835%	$105.1341	$105.13	$105.15	$105.10
7 purchase totals =	$744.82		$824.3230	$824.32	$824.30	$824.30