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	$248.43	12.800%	$280.229	$280.23	$280.25	$280.20
Purchase #2	$66.91	7.193%	$71.7228	$71.72	$71.70	$71.70
Purchase #3	$163.81	4.519%	$171.2126	$171.21	$171.20	$171.20
Purchase #4	$10.45	9.690%	$11.4626	$11.46	$11.45	$11.50
Purchase #5	$59.44	10.204%	$65.5053	$65.51	$65.50	$65.50
Purchase #6	$63.42	10.455%	$70.0506	$70.05	$70.05	$70.10
Purchase #7	$82.31	8.678%	$89.4529	$89.45	$89.45	$89.50
7 purchase totals =	$694.77		$759.6358	$759.63	$759.60	$759.70