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	$29.43	7.141%	$31.5316	$31.53	$31.55	$31.50
Purchase #2	$97.89	6.579%	$104.3302	$104.33	$104.35	$104.30
Purchase #3	$142.68	9.343%	$156.0106	$156.01	$156.00	$156.00
Purchase #4	$185.46	6.470%	$197.4593	$197.46	$197.45	$197.50
Purchase #5	$21.68	12.624%	$24.4169	$24.42	$24.40	$24.40
Purchase #6	$135.82	5.669%	$143.5196	$143.52	$143.50	$143.50
Purchase #7	$68.98	13.797%	$78.4972	$78.50	$78.50	$78.50
7 purchase totals =	$681.94		$735.7654	$735.77	$735.75	$735.70