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	$237.81	12.223%	$266.8775	$266.88	$266.90	$266.90
Purchase #2	$107.26	6.770%	$114.5215	$114.52	$114.50	$114.50
Purchase #3	$203.88	10.780%	$225.8583	$225.86	$225.85	$225.90
Purchase #4	$120.40	13.690%	$136.8828	$136.88	$136.90	$136.90
Purchase #5	$52.97	11.692%	$59.1633	$59.16	$59.15	$59.20
Purchase #6	$40.54	8.585%	$44.0204	$44.02	$44.00	$44.00
Purchase #7	$139.83	12.147%	$156.8152	$156.82	$156.80	$156.80
7 purchase totals =	$902.69		$1,004.1390	$1,004.14	$1,004.10	$1,004.20