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	$225.64	13.754%	$256.6745	$256.67	$256.65	$256.70
Purchase #2	$112.29	9.692%	$123.1731	$123.17	$123.15	$123.20
Purchase #3	$11.38	8.237%	$12.3174	$12.32	$12.30	$12.30
Purchase #4	$181.79	9.259%	$198.6219	$198.62	$198.60	$198.60
Purchase #5	$136.37	4.496%	$142.5012	$142.50	$142.50	$142.50
Purchase #6	$32.90	12.653%	$37.0628	$37.06	$37.05	$37.10
Purchase #7	$86.90	10.322%	$95.8698	$95.87	$95.85	$95.90
7 purchase totals =	$787.27		$866.2207	$866.21	$866.10	$866.30