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	$6.31	7.373%	$6.7752	$6.78	$6.80	$6.80
Purchase #2	$90.87	3.461%	$94.015	$94.02	$94.00	$94.00
Purchase #3	$202.39	6.688%	$215.9258	$215.93	$215.95	$215.90
Purchase #4	$55.54	11.222%	$61.7727	$61.77	$61.75	$61.80
Purchase #5	$146.59	4.410%	$153.0546	$153.05	$153.05	$153.10
Purchase #6	$161.31	9.472%	$176.5893	$176.59	$176.60	$176.60
Purchase #7	$137.78	4.240%	$143.6219	$143.62	$143.60	$143.60
7 purchase totals =	$800.79		$851.7545	$851.76	$851.75	$851.80