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	$33.78	12.618%	$38.0424	$38.04	$38.05	$38.00
Purchase #2	$211.34	13.323%	$239.4968	$239.50	$239.50	$239.50
Purchase #3	$213.85	9.406%	$233.9647	$233.96	$233.95	$234.00
Purchase #4	$227.53	3.750%	$236.0624	$236.06	$236.05	$236.10
Purchase #5	$11.77	13.153%	$13.3181	$13.32	$13.30	$13.30
Purchase #6	$34.46	10.436%	$38.0562	$38.06	$38.05	$38.10
Purchase #7	$101.60	10.128%	$111.89	$111.89	$111.90	$111.90
7 purchase totals =	$834.33		$910.8306	$910.83	$910.80	$910.90