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	$34.38	11.133%	$38.2075	$38.21	$38.20	$38.20
Purchase #2	$91.30	13.401%	$103.5351	$103.54	$103.55	$103.50
Purchase #3	$80.73	12.656%	$90.9472	$90.95	$90.95	$90.90
Purchase #4	$59.98	8.352%	$64.9895	$64.99	$65.00	$65.00
Purchase #5	$38.75	7.471%	$41.645	$41.65	$41.65	$41.60
Purchase #6	$123.60	12.382%	$138.9042	$138.90	$138.90	$138.90
Purchase #7	$43.80	12.536%	$49.2908	$49.29	$49.30	$49.30
7 purchase totals =	$472.54		$527.5193	$527.53	$527.55	$527.40