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	$82.30	8.375%	$89.1926	$89.19	$89.20	$89.20
Purchase #2	$14.51	9.210%	$15.8464	$15.85	$15.85	$15.80
Purchase #3	$185.67	6.659%	$198.0338	$198.03	$198.05	$198.00
Purchase #4	$97.45	7.543%	$104.8007	$104.80	$104.80	$104.80
Purchase #5	$43.68	6.553%	$46.5424	$46.54	$46.55	$46.50
Purchase #6	$117.32	11.602%	$130.9315	$130.93	$130.95	$130.90
Purchase #7	$95.99	3.288%	$99.1462	$99.15	$99.15	$99.10
7 purchase totals =	$636.92		$684.4936	$684.49	$684.55	$684.30