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	$138.49	8.740%	$150.594	$150.59	$150.60	$150.60
Purchase #2	$101.30	6.173%	$107.5532	$107.55	$107.55	$107.60
Purchase #3	$173.30	10.258%	$191.0771	$191.08	$191.10	$191.10
Purchase #4	$103.56	7.751%	$111.5869	$111.59	$111.60	$111.60
Purchase #5	$247.64	13.240%	$280.4275	$280.43	$280.45	$280.40
Purchase #6	$85.89	9.792%	$94.3003	$94.30	$94.30	$94.30
Purchase #7	$97.97	10.321%	$108.0815	$108.08	$108.10	$108.10
7 purchase totals =	$948.15		$1,043.6205	$1,043.62	$1,043.70	$1,043.70