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	$94.95	6.360%	$100.9888	$100.99	$101.00	$101.00
Purchase #2	$37.94	12.344%	$42.6233	$42.62	$42.60	$42.60
Purchase #3	$86.50	10.370%	$95.4701	$95.47	$95.45	$95.50
Purchase #4	$20.30	3.147%	$20.9388	$20.94	$20.95	$20.90
Purchase #5	$220.76	4.831%	$231.4249	$231.42	$231.40	$231.40
Purchase #6	$242.35	11.124%	$269.309	$269.31	$269.30	$269.30
Purchase #7	$146.65	8.278%	$158.7897	$158.79	$158.80	$158.80
7 purchase totals =	$849.45		$919.5446	$919.54	$919.50	$919.50