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	$92.69	7.157%	$99.3238	$99.32	$99.30	$99.30
Purchase #2	$105.93	10.268%	$116.8069	$116.81	$116.80	$116.80
Purchase #3	$250.36	12.170%	$280.8288	$280.83	$280.85	$280.80
Purchase #4	$157.33	9.863%	$172.8475	$172.85	$172.85	$172.80
Purchase #5	$208.67	5.454%	$220.0509	$220.05	$220.05	$220.10
Purchase #6	$138.83	12.791%	$156.5877	$156.59	$156.60	$156.60
Purchase #7	$192.61	5.168%	$202.5641	$202.56	$202.55	$202.60
7 purchase totals =	$1,146.42		$1,249.0097	$1,249.01	$1,249.00	$1,249.00