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	$82.53	9.642%	$90.4875	$90.49	$90.50	$90.50
Purchase #2	$50.80	12.373%	$57.0855	$57.09	$57.10	$57.10
Purchase #3	$168.52	10.588%	$186.3629	$186.36	$186.35	$186.40
Purchase #4	$131.52	10.247%	$144.9969	$145.00	$145.00	$145.00
Purchase #5	$24.86	8.726%	$27.0293	$27.03	$27.05	$27.00
Purchase #6	$137.72	11.700%	$153.8332	$153.83	$153.85	$153.80
Purchase #7	$114.61	11.797%	$128.1305	$128.13	$128.15	$128.10
7 purchase totals =	$710.56		$787.9258	$787.93	$788.00	$787.90