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	$150.54	3.161%	$155.2986	$155.30	$155.30	$155.30
Purchase #2	$248.82	12.584%	$280.1315	$280.13	$280.15	$280.10
Purchase #3	$65.78	6.694%	$70.1833	$70.18	$70.20	$70.20
Purchase #4	$111.88	7.128%	$119.8548	$119.85	$119.85	$119.90
Purchase #5	$18.37	11.217%	$20.4306	$20.43	$20.45	$20.40
Purchase #6	$45.47	4.251%	$47.4029	$47.40	$47.40	$47.40
Purchase #7	$74.52	12.375%	$83.7419	$83.74	$83.75	$83.70
7 purchase totals =	$715.38		$777.0436	$777.03	$777.10	$777.00