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	$231.32	12.224%	$259.5966	$259.60	$259.60	$259.60
Purchase #2	$151.98	12.517%	$171.0033	$171.00	$171.00	$171.00
Purchase #3	$89.54	6.269%	$95.1533	$95.15	$95.15	$95.20
Purchase #4	$33.75	3.353%	$34.8816	$34.88	$34.90	$34.90
Purchase #5	$20.94	10.521%	$23.1431	$23.14	$23.15	$23.10
Purchase #6	$29.40	10.848%	$32.5893	$32.59	$32.60	$32.60
Purchase #7	$78.63	5.819%	$83.2055	$83.21	$83.20	$83.20
7 purchase totals =	$635.56		$699.5727	$699.57	$699.60	$699.60