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	$99.77	12.858%	$112.5984	$112.60	$112.60	$112.60
Purchase #2	$46.86	4.645%	$49.0366	$49.04	$49.05	$49.00
Purchase #3	$98.35	12.758%	$110.8975	$110.90	$110.90	$110.90
Purchase #4	$219.30	6.593%	$233.7584	$233.76	$233.75	$233.80
Purchase #5	$248.81	12.449%	$279.7844	$279.78	$279.80	$279.80
Purchase #6	$99.32	4.295%	$103.5858	$103.59	$103.60	$103.60
Purchase #7	$112.52	4.249%	$117.301	$117.30	$117.30	$117.30
7 purchase totals =	$924.93		$1,006.9621	$1,006.97	$1,007.00	$1,007.00