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	$46.50	13.583%	$52.8161	$52.82	$52.80	$52.80
Purchase #2	$35.60	5.291%	$37.4836	$37.48	$37.50	$37.50
Purchase #3	$101.56	10.203%	$111.9222	$111.92	$111.90	$111.90
Purchase #4	$12.25	10.365%	$13.5197	$13.52	$13.50	$13.50
Purchase #5	$83.99	13.696%	$95.4933	$95.49	$95.50	$95.50
Purchase #6	$202.68	4.515%	$211.831	$211.83	$211.85	$211.80
Purchase #7	$92.41	11.832%	$103.344	$103.34	$103.35	$103.30
7 purchase totals =	$574.99		$626.4099	$626.40	$626.40	$626.30