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	$226.90	12.655%	$255.6142	$255.61	$255.60	$255.60
Purchase #2	$66.47	8.217%	$71.9318	$71.93	$71.95	$71.90
Purchase #3	$137.60	4.624%	$143.9626	$143.96	$143.95	$144.00
Purchase #4	$10.45	4.659%	$10.9369	$10.94	$10.95	$10.90
Purchase #5	$181.77	8.462%	$197.1514	$197.15	$197.15	$197.20
Purchase #6	$101.83	10.641%	$112.6657	$112.67	$112.65	$112.70
Purchase #7	$228.34	13.511%	$259.191	$259.19	$259.20	$259.20
7 purchase totals =	$953.36		$1,051.4536	$1,051.45	$1,051.45	$1,051.50