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	$181.33	5.236%	$190.8244	$190.82	$190.80	$190.80
Purchase #2	$225.48	4.504%	$235.6356	$235.64	$235.65	$235.60
Purchase #3	$92.29	5.397%	$97.2709	$97.27	$97.25	$97.30
Purchase #4	$80.82	10.151%	$89.024	$89.02	$89.00	$89.00
Purchase #5	$131.71	6.800%	$140.6663	$140.67	$140.65	$140.70
Purchase #6	$56.60	11.637%	$63.1865	$63.19	$63.20	$63.20
Purchase #7	$138.53	4.159%	$144.2915	$144.29	$144.30	$144.30
7 purchase totals =	$906.76		$960.8992	$960.90	$960.85	$960.90