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	$232.90	13.492%	$264.3229	$264.32	$264.30	$264.30
Purchase #2	$106.75	10.608%	$118.074	$118.07	$118.05	$118.10
Purchase #3	$185.80	13.231%	$210.3832	$210.38	$210.40	$210.40
Purchase #4	$100.28	4.839%	$105.1325	$105.13	$105.15	$105.10
Purchase #5	$113.52	4.861%	$119.0382	$119.04	$119.05	$119.00
Purchase #6	$212.40	5.679%	$224.4622	$224.46	$224.45	$224.50
Purchase #7	$213.80	13.572%	$242.8169	$242.82	$242.80	$242.80
7 purchase totals =	$1,165.45		$1,284.2299	$1,284.22	$1,284.20	$1,284.20