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	$245.87	5.357%	$259.0413	$259.04	$259.05	$259.00
Purchase #2	$80.86	3.348%	$83.5672	$83.57	$83.55	$83.60
Purchase #3	$28.98	8.280%	$31.3795	$31.38	$31.40	$31.40
Purchase #4	$92.69	7.687%	$99.8151	$99.82	$99.80	$99.80
Purchase #5	$245.87	4.155%	$256.0859	$256.09	$256.10	$256.10
Purchase #6	$56.43	9.530%	$61.8078	$61.81	$61.80	$61.80
Purchase #7	$108.55	3.119%	$111.9357	$111.94	$111.95	$111.90
7 purchase totals =	$859.25		$903.6325	$903.65	$903.65	$903.60