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	$37.36	9.339%	$40.8491	$40.85	$40.85	$40.80
Purchase #2	$84.68	5.661%	$89.4737	$89.47	$89.45	$89.50
Purchase #3	$130.85	10.293%	$144.3184	$144.32	$144.30	$144.30
Purchase #4	$128.47	4.677%	$134.4785	$134.48	$134.50	$134.50
Purchase #5	$178.55	11.248%	$198.6333	$198.63	$198.65	$198.60
Purchase #6	$223.76	4.367%	$233.5316	$233.53	$233.55	$233.50
Purchase #7	$116.93	8.141%	$126.4493	$126.45	$126.45	$126.40
7 purchase totals =	$900.60		$967.7339	$967.73	$967.75	$967.60