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	$136.55	10.178%	$150.4481	$150.45	$150.45	$150.40
Purchase #2	$77.83	7.710%	$83.8307	$83.83	$83.85	$83.80
Purchase #3	$172.92	4.761%	$181.1527	$181.15	$181.15	$181.20
Purchase #4	$21.86	4.850%	$22.9202	$22.92	$22.90	$22.90
Purchase #5	$200.25	11.219%	$222.716	$222.72	$222.70	$222.70
Purchase #6	$142.35	8.173%	$153.9843	$153.98	$154.00	$154.00
Purchase #7	$65.71	13.783%	$74.7668	$74.77	$74.75	$74.80
7 purchase totals =	$817.47		$889.8188	$889.82	$889.80	$889.80