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	$115.97	13.422%	$131.5355	$131.54	$131.55	$131.50
Purchase #2	$7.75	9.733%	$8.5043	$8.50	$8.50	$8.50
Purchase #3	$94.32	3.433%	$97.558	$97.56	$97.55	$97.60
Purchase #4	$55.58	5.272%	$58.5102	$58.51	$58.50	$58.50
Purchase #5	$230.94	12.601%	$260.0407	$260.04	$260.05	$260.00
Purchase #6	$36.33	13.642%	$41.2861	$41.29	$41.30	$41.30
Purchase #7	$53.51	6.795%	$57.146	$57.15	$57.15	$57.10
7 purchase totals =	$594.40		$654.5808	$654.59	$654.60	$654.50